Engine Performance during Transient and Steady-State Operation

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Engine performance during transient and steady-state operation with oxygenated fuels Ali Zare, Timothy A Bodisco, Md. Nurun Nabi, Farhad M. Hossain, Zoran Danil Ristovski, and Richard J. Brown Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 06 Jun 2017 Downloaded from http://pubs.acs.org on June 10, 2017

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Engine performance during transient and steady-state operation with

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oxygenated fuels

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Ali Zarea,*, Timothy A. Bodiscob, Md Nurun Nabic, Farhad M. Hossaina, Zoran D. Ristovskia,d, Richard J.

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Browna

6 a

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Biofuel Engine Research Facility, Queensland University of Technology (QUT), QLD 4000, Australia b

8 c

9 10 11

d

School of Engineering, Deakin University, VIC 3216, Australia

School of Engineering and Technology, Central Queensland University, Perth, WA 6000, Australia

International Laboratory for Air Quality and Health, Queensland University of Technology (QUT), QLD 4000, Australia

12 13

Abstract

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Owing to the increasing share of biofuels in combustion engines, use of these oxygenated fuels

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instead of diesel should be evaluated under different engine operating conditions. This paper

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studies the influence of oxygenated fuels on engine performance parameters under transient,

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compared to steady-state, operation on a six-cylinder, turbocharged, compression-ignition engine

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with a common rail injection system. The fuels used in this study were diesel, waste cooking

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biodiesel and triacetin (as a highly oxygenated additive). A custom test was used to investigate

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different engine performance parameters during acceleration, load increase and steady-state

21

modes of operation. Additionally, a legislative transient cycle (NRTC)—composed of many

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discrete transient modes—was used to study engine performance during a whole transient cycle.

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In this paper, different engine performance-related parameters were investigated, such as IMEP, 1 ACS Paragon Plus Environment

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BMEP, FMEP, turbocharger lag, air-to-fuel ratio, engine speed and torque, start of injection,

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start of combustion, injection pressure, maximum in-cylinder pressure, maximum rate of

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pressure rise, intake and exhaust manifold pressures and CoV of IMEP. The investigation

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demonstrates that engine behaviour during transient operation is different from steady-state

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operation. Results during NRTC indicated that, in comparison with diesel, the oxygenated fuels

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have lower IMEP (up to 18.7 %), BMEP (up to 21.7 %) and FMEP (up to 12.7 %). During

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transient modes of the custom test, using oxygenated fuels rather than diesel resulted in higher

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indicated torque, maximum in-cylinder pressure and maximum rate of pressure rise; however,

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during steady-state, most of the oxygenated fuels had lower values in these three parameters.

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Each advance in SOI corresponds to a rise in the maximum in-cylinder pressure and in the

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maximum rate of pressure rise. Oxygenated fuels had lower intake manifold pressure and CoV of

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IMEP than diesel. Different fuel properties were used to interpret engine behaviour.

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Keywords: Turbocharger lag; fuel oxygen; biodiesel; driving cycle; acceleration; load increase.

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1. Introduction

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After more than 20 years of UN negotiations, universal agreement was reached at the 2015 Paris

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Climate Conference (COP21) to keeping global warming below 2°C. An implication of this

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decision is that it will lead to a decrease in the use of fossil fuels, which are significant

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contributors to global warming.1 A reduction in fossil fuels can be achieved by finding new fuel

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sources such as biofuels.

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Among the different types of biofuels, waste cooking biodiesel has attracted attention because of

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its close properties to diesel, low price, and global availability.2, 3 Waste cooking oil, used as a

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source of fuel, can also help solve disposal issues with this waste material (e.g. dumping into 2 ACS Paragon Plus Environment

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rivers). In the US and EU markets rapeseed and soybean oil are widely used as a feedstock for

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the production of biodiesel.4 However, in the Australian context waste cooking oil biodiesel is

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dominant. A comparison between these widely used biodiesels showed that three fatty acids

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(Palmitic acid, Oleic acid and Linoleic acid) are present at levels greater than 10% in waste

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cooking oil and soybean oil.5, 6 Also, in the case of rapeseed oil two fatty acids are above 10%

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(Oleic acid and Linoleic acid). In addition, three fatty acids (Palmitic acid, Oleic acid and

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Linoleic acid) make up ~94% of waste cooking biodiesel. The same fatty acids in rapeseed and

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soybean oil make up ~86 and ~88% of their content, respectively. Therefore, engine performance

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and emissions of waste cooking oil are representative of that for rapeseed and soybean oil.

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Kulkarni and Dalai3, when reviewing the advantages and disadvantages of waste cooking oil as a

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source for biodiesel, reported lower PM emissions and higher NOx emissions. Another study

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demonstrated that use of this biofuel decreased CO and CO2 while increasing brake-specific fuel

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consumption and NO2.7 The lower heating value of this type of fuel, compared to diesel, was

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reported to be the reason for increased fuel consumption and decreased brake power.8

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In comparison with diesel, which has no oxygen content, the oxygen content of biodiesel has a

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significant influence on engine performance and emissions.9-14 Oxygen content in biodiesel

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relates to the fatty acid ester profile, such as carbon chain length and unsaturation level.15

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Because fuel oxygen content is a major factor in emission reduction, use of a low volume of a

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highly-oxygenated additive can significantly increase the blend oxygen content and consequently

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decrease emission.

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Triacetin [C9H14O6]—a triester of glycerol acetic acid—has a high oxygen content and can be

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used as an oxygenated additive in the combustion process.16, 17 The production of this glycerol-

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derived fuel increases with the production of biofuel, glycerol being a reaction byproduct of the 3 ACS Paragon Plus Environment

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biodiesel transesterification process. Casas et al.16 reported that adding triacetin to biofuel

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increases the viscosity and oxygen content and decreases the heating value and cetane number of

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the fuel. A limited number of studies, mostly from our research group, have used triacetin as a

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fuel additive in combustion engines under steady-state operating modes.18-22

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Owing to the disadvantages of using fossil fuels and the advantages of biofuels1, the EU issued

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Directive 2009/28/EC to increase the share of renewable biofuels in the transportation sector to

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10% by 2020. An increasing market share of biofuels gives the impression that the advantages of

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using these fuels surpass the disadvantages. However, such evaluation should be conducted

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under different engine operating conditions to quantify advantages and disadvantages; such

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quantification is essential for evaluating the possibility of using these alternative fuels in the

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market.

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To date, most studies of internal combustion engines have focused on steady-state operation.1

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However, vehicle engines are seldom used in steady state.23 Therefore, studies that investigate

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transient operation are more likely to provide results that reflect reality than those which only

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investigate steady-state operation. Transient operation is defined here as any operation in which

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fuel injection or engine speed change frequently, in contrast to steady-state operation, in which

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the injected fuel and engine speed remain relatively unchanged.1

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At present, the vast majority of new diesel engines are turbocharged.24 Turbocharging diesel

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engines is beneficial because of reductions in CO2 emission, increment in specific brake power

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and better fuel economy.25 However, the transient operation of turbocharged diesel engines have

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been associated with slow acceleration rates and, subsequently, poor drivability and overshoots

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in combustion products. These could stem from turbocharger lag, which is the most notable off-

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design parameter.26 4 ACS Paragon Plus Environment

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In turbocharged diesel engines, turbocharger lag is defined as a mismatch between the slower

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response of the supplied air by the turbocharger compressor—due to the turbocharger’s moment

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of inertia—and the rapid response of the fuel pump during load (or speed) increase.1 This delay

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time leads to a low AFR (air-to-fuel ratio) and rich combustion, which affects the torque build-

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up, and exhaust emissions which peak over their steady-state counterparts. Since the fuel oxygen

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content can improve the rich combustion, the influence of oxygenated fuels instead of diesel on

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the turbocharger lag side effects should be investigated.

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The complexity of transient operation experiments, and the availability of high-tech fast-

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response measuring instruments and automatically-controlled test-beds, have limited the research

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performed to-date on transient engine operation. A recent literature review by Giakoumis et al.1

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reported that the number of publications investigating the effect of biodiesel during transient

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operation is very limited in comparison with the investigation of steady-state operation. They

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also showed that almost all of the work to-date on transient operation focused on transient cycles,

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analysing their measurements in a quasi-steady-state manner, showing the mean and cumulative

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values of engine performance and exhaust emissions, as dictated by legislated drive cycle

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procedures. This consequently conceals the effect of individual engine speed and load changes.27

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Therefore, separately studying the transient engine performance and emissions for each

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acceleration and load acceptance is of importance for revealing the transient operation

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mechanism. However, only a small proportion of publications on transient operation have

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studied the discrete modes of transient operation, such as acceleration and load acceptance1, and

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their main focus was exhaust emissions rather than engine performance.

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Rakopoulos et al.27 investigated the effects of diesel, biodiesel and n-butanol during transient and

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steady-state conditions. This study demonstrated that turbocharger lag caused an overshoot in 5 ACS Paragon Plus Environment

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NO and smoke opacity for all the tested fuels. Overshoot in NO with diesel was lower when

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compared to the other fuels, while diesel had the highest overshoot in smoke opacity compared

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to other fuel. The maximum cylinder pressure with the tested fuels peaked over the steady-state

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counterpart during turbocharger lag. This study also displayed the engine speed, turbocharger

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speed and boost pressure during acceleration. It indicated that diesel had higher response rates

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compared to n-butanol blend. A study by Rakopoulos et al.23 returned different engine

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performance parameters, NO and smoke opacity during three different acceleration and load

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increase modes when using a turbocharged diesel engine. The fuels used in their study were

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diesel, biodiesel and n-butanol. It indicated turbocharger lag as the reason for overshoots in NO,

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smoke opacity and maximum cylinder pressure. In addition, the maximum global gas

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temperature in cylinder for the tested fuels was used to interpret the NOx behaviour. There are

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some other studies in the literature on different transient discrete modes.22-24, 26, 28, 29

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A thorough literature search could not identify any publication that used waste cooking biodiesel

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and triacetin to study transient engine performance. This paper studies the effect of oxygenated

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fuels on engine performance parameters during transient operation, compared to steady-state

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operation, using a range of fuels containing 0 to 14.23 wt% oxygen that are based on diesel,

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waste cooking biodiesel and triacetin. This research uses a custom test which has been designed

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to investigate acceleration and load increase at discrete transient modes and the corresponding

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end steady-state mode of operation for each transient mode. The results from the discrete

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transient modes can be correlated against a continuously transient cycle. Hence, a legislative

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transient cycle is used to study engine performance during a whole transient cycle which is

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composed of many discrete transient modes.

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2. Materials and methods

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2.1

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The engine used in this study was a six-cylinder turbocharged compression-ignition engine with a

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common rail injection system coupled to an in-house electronically-controlled water brake

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dynamometer controlling the transient and steady-state engine load during the tests. This custom

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in-house hydraulic brake has very sensitive control of pressure and flow—the accuracy of the

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dynamometer is within 0.5%. Table 1 shows the test engine specifications. This engine research

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facility has the ability to program different modal and transient cycles that can be run

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automatically. Figure 1 illustrates the schematic diagram of the test setup in this experimental

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study.

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In-cylinder pressure was obtained with a piezoelectric transducer (Kistler 6053CC60,

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manufacturer stated sensitivity of ≈ -20 pC/bar) connected to a simultaneous analogue-to-digital

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converter (Data Translation DT9832) which was used to collect the crank angle sensor (Kistler

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type 2614, manufacturer stated resolution of 0.5 crank angle degrees) and fuel injection data. The

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fuel injection information was obtained by directly interrogating the electric signal at the first

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injector, as described by Bodisco et al..30 The data acquisition uses an in-house LabVIEW

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program, which stores the large datasets in binary format. Further processing is done using in-

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house Matlab code to obtain in-cylinder (indicated) parameters. Readers can also refer to

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Bodisco and Brown31 for more information.

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The calibration of the engine can have a huge impact on engine performance and emissions

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trends with alternative fuels32, especially under transient operation.1 This study has been

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performed on a diesel-tuned engine and the same engine calibration from the manufacturer was

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used for all the tested fuels. Some disadvantages could arise due to calibration issues. Whilst it is

Experimental facilities


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possible that multiple recalibrations aimed at optimizing the operation of each fuel might change

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the results and mitigate some of the disadvantages of using oxygenated fuels, in practice biofuels

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are likely to be primarily used in diesel-tuned calibrated engines.1

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Table 1. Test engine specifications Model

Cummins ISBe220 31165

Emission standard

Euro III

Cylinders

6 in-line

Capacity

5.9 L

Aspiration

Turbocharged

Maximum torque

820 Nm @ 1500 rpm

Bore × stroke

102 × 120 (mm)

Maximum power

162 kW @ 2500 rpm

Compression ratio

17.3:1

Dynamometer type

Hydraulic

Fuel injection

High pressure common rail

166 167 168 169 170

171

172 173

Figure 1. Schematic of experimental setup


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2.2

Fuel selection

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Six fuels were used in this study: D100 (100% diesel), B100 (100% waste cooking biodiesel),

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D60B35T5 (60%, 35% and 5% blend of diesel, waste cooking biodiesel and triacetin,

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respectively), B96T04 (blend of 96% waste cooking biodiesel and 4% triacetin), T8B92 (blend

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of 92% waste cooking biodiesel and 8% triacetin) and T10B90 (blend of 90% waste cooking

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biodiesel and 10% triacetin). The abovementioned blending ratios were presented by volume.

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The miscibility test was done at room temperature for 96 hours, during which no phase

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separation occurred.

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Table 2 displays the tested fuel properties. It shows the fuel oxygen content range at 0 to 14.23

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wt%. The table shows that the lower heating value (LHV) of fuels decreases with fuel oxygen

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content, which in turn has a negative influence on engine power. Increasing fuel oxygen content

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is also associated with increased viscosity of fuel, which in turn leads to poor atomisation during

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combustion.1 The blends listed in Table 2 are calculated based on D100, B100 and T100. Fuel

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properties for D100, B100 and T100 were measured based on standard methods. For example,

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ASTM D445 was used to measure the fuel viscosity for D100 and B100. Fuel technical

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specification for D100, B100 and T100 can be found in Appendices A1, A2 and A3,

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respectively. The reader can refer to Casas et al.16 for more information about triacetin. In

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addition, more detailed information about waste cooking biodiesel can be found in a recent

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publication from our research group.6 It reported, for example, that the physical and chemical

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properties of B100 were measured based on biodiesel standards EN 14214 and ASTM 6751-12.

194 195


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Table 2. Fuel properties Fuel

D100

D60B35T5

B100

T4B96

T8B92

T10B90

T100

O (wt%)

0

6.02

10.93

12.25

13.57

14.23

44.00

H (wt%)

14.8

13.47

12.21

11.97

11.74

11.63

6.42

C (wt%)

85.1

80.46

76.93

75.81

74.73

74.19

49.53

LHV (MJ/kg)

41.77

38.92

37.2

36.38

35.57

35.16

16.78

HHV (MJ/kg)

44.79

41.74

39.9

39.02

38.15

37.72

18.08

Density @ 15°C (g/cc)

0.84

0.866

0.87

0.882

0.893

0.898

1.159

Cetane number

53.3

53.24

58.6

56.86

55.11

54.24

15

Kinematic viscosity @ 40°C (mm2/s)

2.64

3.66

4.82

4.94

5.06

5.12

7.83

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2.3

Design of experiment

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In this study, the Non-Road Transient Cycle (NRTC), shown in Figure 2, was used to investigate

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the effect of oxygenated fuel on engine performance during a transient cycle. The rationale

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behind selecting this cycle, as opposed to other transient cycles, was the high frequency of abrupt

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speed and load changes. The NRTC is generally considered one of the more aggressive cycles

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because of its highly non-stationary nature can cause all of the fuels to exhibit larger transient

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effects than they would be expected to have in typical on-highway operation. Comparison of the

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results with actual on-road driving cannot directly be made because of the very variable nature of

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driving conditions including changes in gradient, aerodynamic drag, wind, traffic conditions and

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driver behaviour. This transient driving cycle was developed by a collaboration between the US

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EPA and authorities in the EU to regulate the emission from mobile non-road engines.33

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Homologation testing using the NRTC is required by a number of emission standards for non-

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road engines, including the US EPA Tier 4 rule, the EU Stage III/IV regulation and Japanese

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2011/13 regulations.


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Speed %

Load %

100

Normalised value (%)

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50

25

0 0

400

800

1200

Time (s)

212 213

Figure 2. NRTC (Non-Road Transient Cycle) schedule

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By definition, transient driving cycles are characterised by frequent changes in speed and load

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profile, thereby limiting their research value into the fundamentals of transient response. Hence,

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a custom quasi-steady-state test that contains acceleration and load increases at discrete modes,

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followed by steady-state operation, aids the fundamental study into transient and steady-state

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operation.

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Amongst the research studies on transient operation, only a limited number use a custom-made

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test for fundamental study into load increase and acceleration discrete transient operation

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modes.23, 27, 28, 34, 35 Using basic concepts from previous transient tests in the literature, a custom

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test—based on a modal driving cycle schedule with some added transient load increase and

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acceleration modes21—was used to investigate engine performance (in this study) and exhaust

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emissions22 during acceleration, load increase and steady-state modes.

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Zare et al.21 introduced a custom drive cycle, based on the European Stationary Cycle (ESC), to

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investigate the steady-state effect of oxygenated fuels. Zare et al.22 extended this study to 11 ACS Paragon Plus Environment

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investigate the emissions during the transient acceleration and load increase modes of the cycle.

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Additionally, deeper investigation into the engine performance characteristics under the transient

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modes of the cycle has been undertaken for this study.

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In this custom test, the speed and load were chosen from ESC because the engine used in this

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investigation had a Euro III emission certification and ESC is a legislated test cycle used in the

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Euro III standards.33 The selected engine loads from ESC were 0%, 25%, 50% and 75%.

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Regarding the selected speeds, apart from the idle condition (approximately 700 rpm), there are

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two other speeds; Speeds A and B are calculated from Equation (1) with units of rpm.33 The nhi

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and nlo are the highest and lowest engine speeds in which 70% and 50% of the maximum power

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occurs, respectively.33 For the engine used in this study the nhi and nlo were 2650 and 1080 rpm. A = nlo + 0.50(nhi - nlo) B = nlo + 0.75(nhi - nlo),

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(1)

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In addition to the defined speeds (A and B), the ESC has another speed (c), which is not used in

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this study. Rather than the sharp change between steady-state modes in ESC, different

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controllable transient ramps were used in this custom test to enable a study of engine

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performance during acceleration and load increase. The concept of adding the ramped modes

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was based on the Supplemental Emissions Test (SET) introduced in the US EPA 2004 emission

245

standards.

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Figure 3 depicts the custom test used in this study. The custom test has two main parts, each

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related to one speed—(a) 1864 or (b) 2257 rpm—including four loads—0%, 25%, 50% and

248

75%. Each part has one acceleration mode and three load increase modes, starting with the idle

249

condition (0% load and 700 rpm), after which acceleration mode begins. In the acceleration

250

mode, at 0% load over five seconds, the engine accelerates from 700 rpm to the target speed,


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either 1864 or 2257 rpm. When the engine achieves the target speed, the load increase mode

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commences and the engine speed remains constant until the end. The first load increase mode

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begins by increasing the load from 0% to 25% over five seconds and then holding the engine

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load at 25% for 30 seconds. The next load increase test starts by increasing the load from 25% to

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50% over 5 seconds and holding the engine load constant at 50% for 30 seconds. Finally, the

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third load increase mode commences by increasing the load from 50% to 75% over five seconds

257

and holding the engine load constant at 75% for 30 seconds. Speed % - - - Load % .........

2300 1900

50

1500

25

1100

0

700 0

(a)

Load (%)

75

Speed (rpm)

100

25

50 75 Time (s)

100

2300

75

1900

50

1500

25

1100

0

100

Speed (rpm)

251

Load (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

700 0

(b)

25

50 75 Time (s)

100

258 259

Figure 3. Custom transient test design in this study at (a) 1865 rpm and (b) 2257 rpm

260

2.4

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Fuel lines were cleaned after changing the fuels during the tests. In this experiment, for the

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cleaning process, first the fuel tank was disconnected and the engine was operated to minimise

263

the amount of fuel in the fuel lines and fuel pumps. Then another fuel tank containing the new

264

fuel was connected and the engine was operated with the new fuel for some hours to make sure

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that all the previous fuel was consumed and only the new fuel is in the system before starting the

266

experiment.

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For each test, at least 60 minutes was allocated to warm the engine, ensuring the reliability of the

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results. The engine used in this study has no after-treatment system (i.e. Exhaust Gas

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Recirculation (EGR), Selective Catalytic Reduction (SCR) or Diesel Particulate Filter (DPF)),

Experimental procedure


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hence no additional preconditioning was needed, thus ensuring the repeatability of the initial

271

conditions. For all the tested fuels, results of the designed test had the same trend as the results

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from the ESC test, which had some similar operating modes. In the custom test, the commanded

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speeds (1865 and 2257 rpm) were selected from ESC. During the experiment, the coefficient of

274

variation (CoV) for the measured speeds was less than 1%. The highest variation at each speed

275

during the experiment was less than 1%.

276

NRTC engine dynamometer schedule and test procedure were adopted from EU DIRECTIVE

277

2004/26/EC. In order to ensure repeatability, NRTC test was conducted three times. The results

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showed that the standard deviation for the engine speed and load over the three repeats were 7.03

279

and 3.17, respectively. Also, the coefficient of variation ((Standard deviation/Average)

280

between the three repeats were 0.58 and 1.45 for the engine speed and load. These low CoV

281

values clearly demonstrate the repeatability of the tests. In addition, the correlation between the

282

commanded speed to the engine and the actual speed from the test was strong, however, in case

283

of engine load that correlation was not as strong as engine speed as the engine used in this study

284

was turbocharged and the turbocharger lag affected the torque build-up.

285

3. Results and discussion

286

This section focuses on the effect of oxygenated fuels on engine operation characteristics during

287

a transient cycle with the NRTC test and during turbocharger lag, acceleration, load increase and

288

steady-state with the custom test detailed in Section 2.3. The method of analysis in this study is

289

to begin by investigating different parameters over the NRTC test. The analysis then continued

290

with only the first part of the custom test, which addressed turbocharger lag by including an

291

acceleration from 700 rpm to the targeted engine speed—(a) 1865 or (b) 2257 rpm—followed by


100)

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Energy & Fuels

292

a load increase from 0% to 25% load, and then remaining at this load and speed for a steady-state

293

period. The effect of fuel properties and transient engine operation are discussed in the analysis.

294

It should be mentioned that, in all the figures, the tested fuels are named according to their

295

oxygen content, and the illustrated data for the six fuels are differentiated by colour.

296

3.1

297

Figure 4 illustrates the brake mean effective pressure (BMEP) during NRTC. As shown, the

298

oxygenated fuels have lower BMEP when compared to that of D100. This is also presented in

299

Figure 5 (a), which depicts the mean value of BMEP over the cycle for the tested fuels. For

300

example, D100 with 0.33 MPa has the highest value and, using oxygenated fuels, can decrease

301

BMEP to 0.26 MPa. As with BMEP, the indicated mean effective pressure (IMEP) with D100 is

302

higher than the other tested fuels. This can be seen in Figure 5 (a), which shows the mean value

303

of IMEP over the NRTC test for the tested fuels. It shows that using oxygenated fuels decreased

304

IMEP mean value by up to 18.7 %.

305

Figure 5 (a) shows that increasing the fuel oxygen content is associated with decreased IMEP

306

and BMEP. This is attributed to the heating value of the fuels36, 37, which decreases with fuel

307

oxygen content. As shown in Table 2, D100 has the highest heating value. Figure 5 (b) shows

308

that IMEP and BMEP increase with LHV of the tested fuels. A high value of R2 (> 0.93) for each

309

trendline shows a strong linear correlation between IMEP/BMEP and LHV.

310

Figure 5 (a) also shows the mean value of friction mean effective pressure (FMEP) over the

311

NRTC test. FMEP is the difference between IMEP and BMEP and indicates engine friction

312

losses. It can be seen from Figure 5 (a) that D100 has the highest FMEP of 0.13 MPa. Use of

313

D60B35T5, B100, T4B96, T8B92 and T10B90, compared to D100, decreased FMEP by 6.4%,

Transient cycle


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

314

5.8%, 8.3%, 11% and 12.7 %, respectively. The change in FMEP could be due to factors such as

315

engine speed and load, lubricating oil and fuel properties.21

316

It has been reported in the literature that the higher lubricity of biodiesel can cause a reduction in

317

friction losses.6, 38-40 Owing to its better lubricity, the use of biodiesel could reduce friction and

318

wear in the high pressure fuel pump.41-43 This is due to the inherent lubrication properties from

319

fatty acid esters.44,

320

caused decreased FMEP in a common rail diesel engine.

321

Figure 5 (c) shows that FMEP has an increasing linear correlation (R2 >0.9) with IMEP. For

322

example, the highest FMEP relates to D100, which has the highest IMEP. To further the

323

analysis, the FMEP was normalised by IMEP, as shown in Figure 5 (d). As can be seen, using

324

oxygenated fuels, instead of D100, increases the normalised FMEP. This shows that the engine

325

power has a strong effect on engine friction. Hence, compared to the oxygenated fuels, the higher

326

calorific value of D100 (which leads to a higher engine power) could be a further reason for

327

higher FMEP with D100.

45

Woo et al.38 reported that the higher lubricity of coconut oil biodiesel

328 329


Page 16 of 38

Page 17 of 38

1.2

BMEP (MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.9

0.6

0.3

0 0

400

800 Time (s)

330 331

Figure 4. BMEP during NRTC

332

D100 D60B35T5

B100 T4B96 T8B92 T10B90


1200

Energy & Fuels

333

0.3

0.2

xx xx xx xx xx xx xx xx 0

334

(a)

0.13 0.12

x

x

x

x

x

x

x

x

x

x

xx xx xx xx xx

xx xx xx xx

xx xx xx xx

0.11 0.1

IMEP and BMEP (MPa)

IMEP, BMEP (MPa)

0.4

IMEP FMEP

R² = 0.93

0.32 R² = 0.91 0.24 35

36

37

(b)

0.14

38

39

40

41

42

LHV (MJ/kg)

Normalised FMEP (%)

32 R² = 0.92

335

BMEP

0.4

6.02 10.93 12.25 13.57 14.23 Oxygen content (wt%)

0.13

0.12

0.11 0.37

IMEP

0.48

0.14

FMEP (MPa)

xxxxxx xxxxxxBMEP xxxxxx xxxxxx

0.5

FMEP (MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 38

R² = 0.74 31 30 29 28

0.39

(c)

0.41

0.43

0.45

0.47

0

3

6

9

12

15

Oxygen content (wt%)

IMEP (MPa)

336 337 338

Figure 5. (a) IMEP, BMEP and FMEP vs. fuel oxygen content, (b) IMEP and BMEP vs. LHV, (c) FMEP vs. IMEP and (d) normalised FMEP vs. LHV. The parameters IMEP, BMEP and FMEP are the mean values over the NRTC test.

339

D100 D60B35T5

B100 T4B96 T8B92 T10B90

340 341

3.2

Turbocharger lag

342

Figure 6 illustrates different engine parameters during the first 20 seconds of custom test at (a)

343

1864 and (b) 2257 rpm. Within this 20 seconds, the engine runs at idle condition (0% load and

344

700 rpm) for the first two seconds; then, at 0% load, the engine accelerates from 700 rpm to one

345

of the target speeds: (a) 1864 or (b) 2257 rpm. When the engine speed reaches the target speed, it

346

remains constant and the engine load increases from 0% to 25% and then is held at 25% until the

347

end.


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Energy & Fuels

348

In transient diesel engine operation, turbocharger lag affects the torque pattern. Because the

349

engine crank shaft and turbocharger shaft are not mechanically connected, turbocharger lag

350

occurs after a load (or speed) increase due to the faster response of fuel injection by the fuel

351

pump when compared to the slower response of the supplied air by the turbocharger compressor.

352

This is because supplied air cannot instantaneously match the fuel flow. However, these

353

parameters do match after a number of engine cycles.

354

Turbocharger lag can be observed in Figure 6, where the sub-diagrams illustrate the “throttle”

355

position and boost pressure, representing the fuel injection and supplied air, respectively. The

356

figure shows these parameters during the first 20 seconds of the custom test at both engine

357

speeds for B100. After the initial two seconds, when the engine accelerates from 700 rpm to (a)

358

1864 or (b) 2257 rpm, the “throttle” position increases while the boost pressure remains constant

359

for some seconds and then begins to increase. This delay time is called turbocharger lag. During

360

turbocharger lag—in which the engine is effectively running in naturally aspirated mode—the

361

AFR drops to below its steady-state counterpart. The lack of supplied air—which leads to lower

362

AFR and, consequently, to rich combustion—is a significant issue during transient operation and

363

affects different engine performance parameters. Since boost pressure depends on turbocharger

364

speed, the side effects worsen at low engine speed.1

365 366 367


Energy & Fuels

368

Boost pressure (kPa)

140

130 120 110

120 110

100

100

60

60

45 30 15

45 30 15 0

0 0

(a)

369

130

Throttle position (%)

Boost pressure (kPa)

140

Throttle position (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 38

5

10 Time (s)

15

0

20

5

(b)

10 Time (s)

15

20

370 371

Figure 6. Development of engine parameters during the first 20 seconds of custom test at (a) 1865 rpm and (b) 2257 rpm

372

0% O2 6.02% O2 10.93% O2

12.25% O2 13.57% O2

14.23% O2

373 374

Figure 7 shows different engine in-cylinder parameters during the first 200 engine cycles of the

375

custom test at (a) 1865 rpm and (b) 2257 rpm for all the tested fuels. This duration corresponds

376

to the first 16.8 s at 1865 rpm and 15.2 s at 2257 rpm in Figure 6, which shows the parameters

377

during idle, acceleration, load increase, and steady state (25% load) modes of the custom test.

378

3.3

379

The turbocharger lag affects engine speed and load response. This is shown in Figure 7, where

380

engine speed increases from idle to (a) 1865 and (b) 2257 rpm, and the indicated torque increases

381

moderately. At the end of the acceleration mode, where the indicated torque increases rapidly,

382

engine speed drops from its peak point to the steady-state value. The overshoot at (a) 1865 rpm

383

ranges from 1973 to 1981 rpm, and at (b) 2257 rpm ranges from 2359 to 2369 rpm.

Engine speed


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Energy & Fuels

384

3.4

Indicated torque

385

Figure 7 illustrates that use of oxygenated fuels rather than D100 during transient modes can

386

have a different result than during steady-state modes. During the steady-state mode under 25%

387

engine load, the indicated torque decreases with fuel oxygen content. For example, the highest

388

and the lowest values at this steady-state mode of the custom test are related to D100 and

389

T10B90 (with the lowest and the highest fuel oxygen contents), respectively. Further analysis

390

revealed the same result at the other steady-state modes of the custom test. This can be seen in

391

Figure 8, which shows the indicated torque during the custom test at (a) 1865 rpm and (b) 2257

392

rpm. This drop is attributable to the heating value of the oxygenated fuel.21, 36, 37 As stated in

393

Table 2, the heating value of the tested fuels decreases with fuel oxygen content.

394

In contrast to the steady-state condition, oxygenated fuels showed higher indicated torque during

395

turbocharger lag and acceleration. This can be seen in the indicated torque sub-diagrams of

396

Figure 7. However, this trend at 2257 rpm is not as clear as 1865 rpm. The reason for higher

397

indicated torque with oxygenated fuels could be due to the fact that, during the transient mode,

398

the AFR is lower than its respective steady-state value and, consequently, the combustion is rich.

399

Hence, the presence of oxygen in the fuel can assist with combustion to move it toward

400

stoichiometric condition in which higher engine power is produced. The fuel oxygen content

401

could not be the only reason for the higher indicated torque with oxygenated fuels, compared to

402

D100. It can be seen that at 1865 rpm, B100 showed the highest indicated torque, although 3

403

fuels had higher oxygen contents.

404


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

405

3.5

Injection parameters

406

Fuel injection strongly influences engine performance and exhaust emissions. With a common

407

rail injection system, such as that used in this study, the injector operates in the time domain,

408

compared to combustion, which occurs in the crank angle domain. Design and tuning parameters

409

of this type of injector are thus significantly affected by engine speed.46

410

Analysing the control signals to the piezo electric diesel injector showed that there is a pilot

411

injection at idle (at 347 crank angle degree) and no pilot and/or post injections at loads of 25%

412

and above regardless of engine speed in this study. Also, analysis on rail pressure at different

413

modes of the custom test showed that the injection pressures at 1865 rpm under 25, 50 and 75%

414

engine load were 58.6, 74.8 and 81.1 MPa, respectively. Also, injection pressures of 69, 86.4 and

415

98.1 MPa were observed at 2257 rpm under 25, 50 and 75% engine load, respectively.

416

To change engine load at a constant speed, where more injected fuel is needed, the ECU changes

417

injection timing parameters, such the start of injection (SOI). SOI can be defined as the point at

418

which injection line pressure reaches injector nozzle-opening-pressure. The SOI parameter is

419

important because it influences combustion characteristics and, consequently, affects engine

420

performance and emissions. It can be observed from Figure 9 that, during steady-state modes of

421

the custom test at 1865 rpm, SOI advances with engine load. In addition to the engine load

422

effect, the SOI analysis in this study revealed that this parameter advances with engine speed

423

from 1865 to 2257 rpm. This parameter is, however, controlled by the injection strategy set by

424

the engine manufacturer.

425

Figure 7, which shows the SOI during the first 200 cycles of the custom test for all the tested

426

fuels, reveals that SOI decreases during the turbocharger lag, then it increases and then stabilises

427

until the end of the acceleration mode. After acceleration by the start of load increase from 0% to 22 ACS Paragon Plus Environment

Page 22 of 38

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Energy & Fuels

428

25%, the SOI crank angle increases sharply to a constant value corresponding to (a) 1865 rpm

429

and (b) 2257 rpm. Figure 10 shows the start of combustion (SOC) during the first 200 cycles of

430

the custom test for all the tested fuels. The start of combustion is considered as the instantaneous

431

ignition of the air and fuel mixture after the ignition delay period. This parameter which leads to

432

a sharp increase in cylinder pressure is influenced by the fuel cetane number. The start of

433

combustion was determined from a band-passed in-cylinder pressure signal using the method

434

described by Bodisco et al.30.

435 436

3.6

Maximum in-cylinder pressure and maximum rate of pressure rise

437

The maximum in-cylinder pressure and maximum rate of pressure rise are influenced by the

438

amount of fuel burnt during the premixed combustion phase. These parameters, which depend

439

greatly on fuel properties, can characterise the fuel’s ability to mix with air and burn.

440

Additionally, the maximum rate of pressure rise can be related to the vibration and engine noise,

441

indicating how fast the in-cylinder pressure is changing in the combustion chamber and

442

impacting on the piston crown, cylinder head and cylinder wall.47

443

Figure 7 shows the maximum in-cylinder pressure and maximum rate of pressure rise during the

444

first 200 cycles of the custom test for all the tested fuels. It can be seen from that figure that there

445

is a correlation between these parameters and SOI, regardless of fuel-type. At both engine

446

speeds, these parameters remain unchanged when SOI is constant. These parameters also change

447

during acceleration and load increase by changing SOI. For example, each advance in SOI

448

corresponds to a rise in the maximum in-cylinder pressure and in the maximum rate of pressure

449

rise.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

450

Figure 7 also indicates variations in the maximum in-cylinder pressure and maximum rate of

451

pressure rise through changing the fuel during transient mode. This could be due to different

452

factors which weaken or reinforce one another under different conditions. One reason for this

453

could be the slight differences between SOI in different fuels during acceleration and load

454

increase (highlighted in the red box), which could result from the transient engine operation.

455

Apart from this reason, fuel properties could be the main reason for the variations in maximum

456

in-cylinder pressure and maximum rate of pressure rise. During acceleration and load increase

457

modes, B100 displayed relatively higher maximum in-cylinder pressure and maximum rate of

458

pressure rise in comparison with other tested fuels. A similar trend also can be seen during idle:

459

B100 has the highest values and D100 has relatively low values. Fuel cetane number could be

460

the influential factor here, however, other fuel properties such as LHV could be effective as well.

461

In contrast to transient operation, in which SOI changes and consequently affects the maximum

462

in-cylinder pressure and maximum rate of pressure rise, SOI is constant for all the fuels and has

463

no effect during the steady-state operation. Hence, the variations in these parameters stem from

464

the fuel properties. D100 has a relatively higher maximum rate of pressure rise when compared

465

to the other tested fuels. Figure 7 indicates that D100 has the highest maximum in-cylinder

466

pressure under 25% steady-state engine load at 1865 rpm. One reason for this could be the

467

heating value of the tested fuel. As shown in Table 2, D100 has the highest heating value

468

between the other tested fuels. Hence, compared to D100, the oxygenated fuels produce lower

469

amounts of energy and, therefore, lower maximum in-cylinder pressure. Figure 11 shows the

470

maximum in-cylinder pressure and maximum rate of pressure rise at steady-state modes of the

471

custom test. During all modes of the custom test—except 25% load at 2257 rpm—D100 has the

472

highest maximum in-cylinder pressure. The figure also shows that, among the tested fuels, D100


Page 24 of 38

Page 25 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

473

has the highest maximum rate of pressure rise during all steady-state modes of the custom test.

474

For example, at 1865 rpm under 50% engine load, D100 with 0.36 MPa, has the highest value.

475

In addition to the heating value, other fuel properties could be influential. At 2257 rpm under

476

25% engine load, B100 has a higher maximum in-cylinder pressure compared to D100, while its

477

LHV is lower than that of D100. This could be due to the higher cetane number of B100

478

compared to D100. At higher engine speeds, where the ignition delay is shorter, the higher

479

cetane number could be more influential. However, as previously mentioned, the variation in

480

maximum in-cylinder pressure and maximum rate of pressure rise could be the result of different

481

mechanisms whose effects can reinforce or cancel each other.

482


Energy & Fuels

Maximum rate of pressure rise (MPa/crank angle degree)

1 0.5

Maximum in-cylinder pressure (MPa)

483

1.5 1 0.5

0

0

8

8



1.5

7 6 5

7 6 5

365 360 355 350 345 340 335

Indicated torque (N.m)

300 250 200 150 100 50 0

Start of injection (crank angle degree)


484 365 360 355 350 345 340 335

486


485

2000 1550 1100 650

487

200 150 100 50 0

2000 1550 1100 650

0

(a)

250

2450 Engine speed (rpm)

2450 Engine speed (rpm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 38

100 Engine cycle

200

0

(b)

100 Engine cycle

200

488 489

Figure 7. Development of engine in-cylinder parameters during the first 200 engine cycles of custom test at (a) 1865 rpm and (b) 2257 rpm

490

D100 D60B35T5

B100 T4B96 T8B92 T10B90



600 450 300 150 0 0

(a)

491

550 1100 Engine cycle

600 450 300 150

1650

0 0

475

(b)


492

Figure 8. Indicated torque during the custom test at (a) 1865 rpm and (b) 2257 rpm

493

D100 D60B35T5

1900

B100 T4B96 T8B92 T10B90


494 365 360 355

362

350 360

345 340 0


495

1650

496

Figure 9. Start of injection during the custom test at 1865 rpm

497

D100 D60B35T5

B100 T4B96 T8B92 T10B90

498

380

Start of combustion (crank angle degree)

Start of combustion (crank angle degree)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels


Page 27 of 38

370 360 350 0

499

50

(a)


380 370 360 350

200

0

(b)

50


200

500 501

Figure 10. Start of combustion during the first 200 engine cycles of custom test at (a) 1865 rpm and (b) 2257 rpm

502

D100 D60B35T5

B100 T4B96 T8B92 T10B90


Energy & Fuels

504

(a)

1865@25 2257@50

9

2257@25 1865@75

1865@50 2257@75


503


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 38

1865@25 2257@50

0.4

2257@25 1865@75

1865@50 2257@75

0.35

8 7

0.3

0.25

6 5 0

3

6 9 12 Oxygen content (wt%)

15

0.2 0

(b)

3 6 9 12 Oxygen content (wt%)

15

505 506

Figure 11. (a) Maximum in-cylinder pressure and (b) maximum rate of pressure rise vs. fuel oxygen content at steady-state modes of the custom test

507

D100 D60B35T5

B100 T4B96 T8B92 T10B90

508 509

3.7

Intake and exhaust manifold pressures

510

Figure 12 (a) shows the intake manifold pressure (measured in-cylinder during the induction

511

stroke) at all the steady-state modes of the custom test for all the tested fuels. As can be seen, this

512

parameters increases with engine load and speed. For example, this parameter has the highest

513

value at 2257 rpm at 75% load, for all the fuels, while the lowest values for all the fuels relate to

514

1865 rpm at 25% load, respectively. Figure 12 (a) also shows that using oxygenated fuels,

515

instead of D100, decreased the intake manifold pressure at all of the modes of the custom test.

516

For example, at 2257 rpm under 75% load, the intake manifold pressure with D100 was 181 kPa,

517

while that for D60B35T5, B100, T4B96, T8B92 and T10B90 were 176, 177, 173, 171 and 169

518

kPa, respectively. Such behaviour is consistent with the lower heating values of the oxygenated

519

fuels resulting in lower engine power and therefore lower intake manifold pressure.

520

Figure 12 (b) shows the exhaust manifold pressure (measured in-cylinder during the exhaust

521

stroke) at all the steady-state modes of the custom test for all the tested fuels. As can be seen, this 28 ACS Paragon Plus Environment

Page 29 of 38

522

parameter increases by increasing the engine speed and load for all the tested fuels. For example,

523

with D100 the exhaust manifold pressure at 1865 rpm under 25, 50 and 75% load are 221, 225

524

and 226 kPa. For the same fuel, this parameter increases from 221 to 228 kPa by increasing the

525

engine speed from 1865 to 2257 rpm under 25% load. At 1865 rpm, between all the tested fuels,

526

D100 has the highest values. It also can be seen that between the oxygenated fuels, increasing the

527

fuel oxygen content is associated with decreased exhaust manifold pressure.

528

529

2257@25 1865@75

1865@50 2257@75

180 160 140 120 100 0

(a)

3


15

1865@25 2257@50

250 Exhaust pressure (kPa)

1865@25 2257@50

200 Intake pressure (kPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

2257@25 1865@75

1865@50 2257@75

240 230 220 210 200 0

(b)

3


15

530 531

Figure 12. (a) Intake and (b) exhaust manifold pressures vs. fuel oxygen content at steady-state modes of the custom test

532

D100 D60B35T5

B100 T4B96 T8B92 T10B90

533 534

3.8

Combustion stability

535

Combustion variability, which can have an adverse effect on engine performance, is dependent

536

on different factors such as AFR variation, mixture composition and its preparation prior to

537

combustion.48 Combustion variability can be indicated by different parameters such as CoV of

538

IMEP.

539

Figure 13 shows the CoV of IMEP at all the steady-state modes of the custom test for all the

540

tested fuels. As can be seen, the CoV of IMEP has higher values at 25% engine load, when 29 ACS Paragon Plus Environment

Energy & Fuels

541

compared to 50 and 75% engine load. For example, the highest value for all the fuels is related

542

to 25% engine load at 2257 rpm. The figure also shows that this parameter increases with engine

543

speed, as it has higher values at 2257 rpm, compared to 1865 rpm. Further analysis revealed that

544

the CoV of IMEP of all the fuels during idle condition is above 8.8 %. Apart from the engine

545

operating condition effect, Figure 13 also shows that the CoV of IMEP decreases when

546

oxygenated fuels are used instead of diesel. For example, at 2257 rpm under 25, 50 and 75%

547

engine load, D100—among all the fuels—has the highest values of 3.49%, 0.99% and 1.54 %,

548

respectively. The reason for this could be that the local conditions during the combustion of the

549

oxygenated fuels are closer to the stoichiometric condition, when compared to that of D100, as

550

the presence of oxygen in the oxygenated fuels facilitates more complete combustion by

551

reducing the local fuel-rich zone within the core region of the sprayed fuel. Further analysis

552

revealed that D100 has the highest CoV of IMEP during idle condition.

553 4 CoV of IMEP (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1865@25 2257@50

2257@25 1865@75

1865@50 2257@75

3 2 1 0 0

554

3

6

9

12

15

Oxygen content (wt%)

555

Figure 13. CoV of IMEP vs. fuel oxygen content at steady-state modes of the custom test

556

D100 D60B35T5

B100 T4B96 T8B92 T10B90

557


Page 30 of 38

Page 31 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

558

4. Summary and Conclusions

559

Owing to the increasing presence of biofuels in combustion engines, the use of oxygenated fuels

560

instead of diesel should be evaluated under different engine operating conditions. This paper

561

studied the effect of oxygenated fuels on transient engine performance, compared to steady-state

562

operation, using a range of fuels with 0 to 14.23 wt% oxygen content, and based on waste

563

cooking biodiesel as the primary fuel and triacetin as a highly-oxygenated additive. This study

564

employed a modern six-cylinder turbocharged common rail diesel engine. It used a custom test

565

to investigate the acceleration and load increase discrete transient modes and the corresponding

566

end steady-state mode of operation. In addition, a legislative transient cycle (NRTC)—composed

567

of many discrete transient modes—was used to study engine performance during a whole

568

transient cycle. In this paper, different engine performance-related parameters were investigated:

569

IMEP, BMEP, FMEP, turbocharger lag, air-to-fuel ratio, engine speed and torque, start of

570

injection, start of combustion, injection pressure, maximum in-cylinder pressure, maximum rate

571

of pressure rise, intake and exhaust manifold pressures, and CoV of IMEP.

572

The following conclusions were drawn:

573

•

574 575

by up to 18.7% and 21.7%, respectively. It also decreased FMEP by up to 12.7%. •

576 577

During NRTC, the use of oxygenated fuels instead of diesel decreased IMEP and BMEP

The use of oxygenated fuels decreased the indicated torque during the steady-state modes while, during transient modes, it generally increased the indicated torque.

•

During transient modes, the use of oxygenated fuels instead of diesel resulted in higher

578

maximum in-cylinder pressure and maximum rate of pressure rise while, during steady-

579

state modes, most of the oxygenated fuels had lower values for these two parameters.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

580

•

581

Each advance in SOI corresponds to a rise in the maximum in-cylinder pressure and in the maximum rate of pressure rise.

582

•

Intake and exhaust manifold pressures increased with engine load and speed

583

•

Oxygenated fuels had lower intake manifold pressure than diesel

584

•

CoV of IMEP during idle and 25% load was higher compared with 50% and 75% load.

585

•

The use of oxygenated fuels rather than diesel decreased the CoV of IMEP.

586

5. Acknowledgement

587

This research was supported by the Australian Research Council’s Linkage Projects funding

588

scheme (project number LP110200158). The authors would like to thank: Mr. Andrew Elder,

589

Mr. Noel Hartnett and Dr. Md. Mostafizur Rahman for their laboratory assistance; Dr. Michael

590

Cholette and Dr. Meisam Babaie for their guidance; Peak3 Pty. Ltd. for assistance with

591

measurement instruments; Mr. James Hurst for providing copyediting and proofreading service;

592

and Eco Tech Biodiesel (Dr. Doug Stuart) for the fuel supply.

593

594

6. Appendices

595

Appendices A1, A2 and A3 show the fuel properties of D100, B100 and T100, respectively.

596 597

6.1

A1. D100

598 599 600 601

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Page 32 of 38

Page 33 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

602 603


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

604

6.2

Page 34 of 38

A1. B100

605 606 607 608 609 610

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Engine Performance during Transient and Steady-State Operation

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