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Combustion
Impact of the pentanol addition and injection timing on the characteristics of a single cylinder diesel engine Mehmet #en, Alaattin Osman Emiroglu, and Ahmet Keskin Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b01759 • Publication Date (Web): 09 Aug 2019 Downloaded from pubs.acs.org on August 12, 2019
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Energy & Fuels
Impact of the pentanol addition and injection timing on the characteristics of a single cylinder diesel engine Mehmet Şena, Alaattin Osman Emiroğlub*, Ahmet Keskina aBolu bBolu
Abant Izzet Baysal University, Department of Automotive Technology, 14100 Bolu, Turkey Abant Izzet Baysal University, Department of Mechanical Engineering, 14100 Bolu, Turkey
Abstract In this study, firstly, the effects of addition of 10% (Pen10), 20% (Pen20) and 30% (Pen30) pentanol on the performance, combustion, and emissions of a diesel engine were investigated. Then, the effect of injection timing for Pen30 fuel was investigated by changing the original injection timing of 20º BTDC to 22º BTDC and 24º BTDC. The engine tests were performed under different loads at 2400 rpm. The results indicated that with the advancing of the diesel injection timing and increasing the pentanol ratio in the fuel blends the ignition delay increased and the start of combustion delayed. The maximum heat release rate and cylinder pressure values of pentanol blends were found higher than those of diesel fuel. Both the maximum cylinder pressure and maximum heat release rate increased with the advancing of the diesel injection timing to 22º and 24º BTDC. BSFC value of Pen30 was higher than that of diesel fuel at the original injection timing and it decreased as the injection timing was advanced to 22º BTDC and 24º BTDC as compared to that of the original injection timing. NOx emission decreased with the increasing pentanol fraction. Also, NOx emissions increased significantly at 24º BTDC injection timing but decreased slightly at 22º BTDC injection timing. Smoke emissions of the pentanol blends are lower than those of the diesel fuel under all operating conditions as well as decreased with the advancing injection timing.
Keywords: Injection timing; Pentanol; Alcohol; Diesel engine; Combustion
*Corresponding author E-mail addresses:
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1. Introduction Diesel engines because of the higher durability, higher torque output and higher fuel-conversion efficiency are unrivaled in heavy-duty machinery, power generation, public transportation, and industrial and agricultural equipment. Although they cause fewer hydrocarbons (HC), carbon dioxide (CO2) and carbon monoxide (CO) than gasoline engines, they emit high nitrogen oxide (NOx) and soot emissions [1]. The reduction in fossil fuel reserves, the increase in energy demands and instability in oil prices force the researchers to investigate alternative renewable biofuels to diesel fuel. Among the biofuels, due to their availability and easy handling and storage, alcohols considered to be the most appealing and good options. The addition of alcohols to diesel fuel has several advantages. Alcohol blends are injected and atomized easily due to their low viscosity. Because of their high oxygen content, low carbon-hydrogen ratio, low sulfur content, alcohols cause less emission, especially soot. Due to the high laminar flame propagation speed, alcohols increase the thermal efficiency of the engine by completing the combustion process earlier. Also, high heat of vaporization of alcohols causes a cooling effect in the intake process, thus increasing the volumetric efficiency [2]. However, the use of lower alcohols which have 3 or less carbon in diesel engines is limited due to the high latent evaporation temperature, low cetane number, hygroscopic nature, poor lubrication, low calorific value and especially poor miscibility with diesel. Higher alcohols containing 4 or more carbons ((C4) butanol, (C5) pentanol, (C6) hexanol, (C8) octanol, etc.) are more suitable for use in diesel engines than lower alcohols because of their higher calorific value, better miscibility, higher cetane number, and less hygroscopic nature [3]. Pentanol has anticorrosive properties and does not influence the fuel system, unlike ethanol and methanol. In the alcohols, pentanol has the closest viscosity, density and latent heat of vaporization to petroleum-based diesel fuel. Pentanol blends are not accepted as flammable because their flashpoint is more than 37.8 °C. Cold filter plugging point properties of pentanol blends are within the EN 116 norms [4]. Pentanol is great renewable alcohol because it can be produced biologically [5-7]. Also, lower alcohols require more energy for their production when compared to pentanol [8]. Campos- Fernández et al. [4] evaluated the n-pentanol/diesel blends effect to diesel engine performance. They concluded that without any engine modification up to 25% of the dieselpentanol blends did not cause any negative effect on engine performance. However, they did not report any emission data. Yilmaz and Atmanli [9] prepared the pentanol blends at different ratio and studied their effects on the exhaust emissions and engine performance of a diesel engine. It was reported that pentanol blends increased the brake specific fuel consumption (BSFC) and decreased the brake thermal efficiency (BTE). The blends of 5% and 35% reduced NOx in opposition to other blends. They also reported that all blends increased HC emission and all blends except 5% increased CO emission. Wei et al. [10] reported that the blends of pentanol up to 30% have no notable difference in engine performance compared to diesel. The addition of pentanol resulted in a decrease in the particulate mass concentration and increase NOx, HC and CO. Sridhar et al. [11] investigated the effects of pentanol blends on emission characteristics and engine performance. The results showed that the pentanol blends could decrease the CO, HC and NOx emissions compared to the diesel fuel with a slight decrease in BTE. These and other studies [3,8,12-20] on pentanol in the literature generally demonstrated that ignition delay (ID) was increased as the alcohol content in the blends increased due to low cetane numbers. Due to the enhanced pre-mixed combustion phase caused by the long ID, the ACS Paragon Plus Environment
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Energy & Fuels
maximum cylinder pressure (CP) and heat release rate (HRR) were increased by the addition of alcohol. With the increased pentanol content in the fuel blends, it was observed that smoke emissions decreased in all engine loads as well as NOx emissions generally decreased at low and medium loads but increased at high loads. There are also some studies in the literature using different higher alcohols such as iso-butanol [21-26], n-hexanol [27,28] and n-octanol [29,30]. As the above-mentioned studies demonstrate, compression-ignition engines are produced to run best with petroleum-based diesel fuel. For other additional fuels such as alcohols, the particular running parameters of the engine such as injection characteristics need to be optimized, taking into account the performance, combustion and emission characteristics [31]. The injection characteristics of the diesel engine including injection delay, static and dynamic injection timing, and duration of injection are the most important operating parameters affecting engine behaviors. The static injection timing is the degree of crank angle at which the pump starts pumping fuel and is always constant. Dynamic injection timing is described as the actual injection timing at which injector start to spray fuel into the cylinder. Dynamic injection timing changes with the physical properties of fuels, such as viscosity, density, and compressibility. The time between static and dynamic injection timing is described as the duration of injection delay [32]. The fuel injection process is important because it affects fuel spray properties and the process of formation of the mixture [33-34]. In the literature, some studies have investigated the impact of injection timing (IT) on the combustion, emission and performance behaviours of a compression ignition engine fed by different alternative fuels [35-38]. Jindal [36] investigated the effect of IT on the combustion, performance and emissions of a small diesel engine fuelled with Jatropha (Jatropha curcas) vegetable oil biodiesel. It was reported that retarding the injection timing by 3 degrees increased the thermal efficiency by about 8 percent and decreased the specific fuel consumption by about 9 percent. Cenk et al. [38] examined the impact of ethanol-diesel mixtures and injection timing on performance and emissions of a small diesel engine. The results indicated that HC and CO emissions were reduced, and CO2 and NOx emissions were increased in both advanced and retarded injection timings. It was also found that changing the injection time reduces BTE and increases BSFC in all fuel mixtures at all engine loads and speeds. The results of these investigations on the change of injection timing generally showed that retarding of the injection timing causes in a shorter ignition delay, lower HRR, and lower peak temperature and pressure. The advancing of the IT of a diesel engine fueled by higher viscosity fuels had a higher HRR and as a result, the thermal efficiency and power output were higher than those of the original injection timing [39]. Furthermore, it was stated that retarded IT often leads to a reduction in power and an increase in brake specific fuel consumption [40]. It was also reported that the advance in IT leads to an increase in NOx emissions and to a decrease in smoke emissions for most fuels [41]. However, there is no detailed study in the literature on the impact of different IT on combustion, performance and emissions of a diesel engine fuelled with pentanol blends. Therefore, in this experimental study, it was focused to investigate the impact of pentanol addition and injection timing on the performance, combustion and emission behaviours of a diesel engine.
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2. Experimental In this study, 10%, 20% and 30% (v/v) pentanol were added to diesel fuel (DF) and named Pen10, Pen 20 and Pen 30 respectively. Some primary properties of diesel fuel and pentanol are shown in Table 1. Table 1. Basic properties of test fuels. Properties Density (kg/m3) Cetan Number Flash Point (°C) Lower heating value (MJ/kg) Kinematics Viscosity (mm2/s) Oxygen (wt %) Carbon (wt %) Hydrogen (wt %)
Diesel Fuel 831.5 58.8 70 43.2 2.4 0 86.6 13.4
Pentanol 814 20 50 34.6 2.8 18.1 68.2 13.6
Figure 1. Schematic picture of the engine test setup. Firstly, the effect of the addition of pentanol on the performance, combustion and exhaust emissions was investigated. Then, the effect of injection time for Pen30 fuel was investigated by increasing the original static injection timing of 20º before top dead center (BTDC) to 22º BTDC and 24º BTDC. The thickness of the pad under the pump was decreased by 0.2 mm, to increase the value of injection advance 2 degree. The engine tests were performed under brake mean effective pressure (BMEP) of 1 bar, 2 bar, 3 bar and 4 bar at the maximum moment engine speed of 2400 rpm. Before collecting the data for all tests the engine was operated until steadystate conditions. The experimental setup is given in Figure 1. The properties of the Lombardini
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Energy & Fuels
15 LD 350 diesel engine used in the experiment are presented in Table 2. The information about the other components used in the experiment is indicated in Table 3. Table 2. The properties of test engine. Items Engine type Cylinder number Maximum torque Maximum power Compression ratio Displacement Bore × stroke Injection pump type Injector type Static injection timing (°CA) Injection nozzle Nozzle opening pressure
Specifications Direct injection, naturally-aspirated, air-cooled 1 16.6 Nm/2400 rpm 7.5 HP/3600 rpm 20.3/1 349 cm3 82 mm × 66 mm Mechanical controlled Single-stage hydro-mechanical 20º BTDC 0.22 × 4 holes × 160 degree 210 bar
The results of cylinder pressure are the mean values of 100 cycle. KiBox Cockpit software uses cylinder pressure mean values for calculations of the combustion characteristics such as the HRR, the start of combustion (crank angle at which 5% of total HRR is obtained), the end of combustion (crank angle at which 90% of total HRR is obtained) and the combustion duration (CD) (crank angle between the start and end of combustion). The dynamic start of injection was taken as the crank angle degree at which the fuel line reaches the injector opening pressure (210 bar). The ignition delay is the difference between the dynamic start of injection and the start of combustion. Table 3. The properties of the test components Component
Brand
Measure
Range
Linearity
Sensitivity
Dynamometer
Kemsan
0-15 kW
0.1 kW
Scale
Ohaus
0-3000 g
0.1 g
Torque meter
Kistler 4550A
Strain gages
0-20 Nm
