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Energy & Fuels 2006, 20, 1460-1470
Experimental Investigation of Optimal Timing of the Diesel Engine Injection Pump Using Biodiesel Fuel Breda Kegl* UniVersity of Maribor, Faculty of Mechanical Engineering, SmetanoVa 17, SI-2000 Maribor ReceiVed December 6, 2005. ReVised Manuscript ReceiVed March 6, 2006
This paper discusses the influence of biodiesel on output characteristics of a diesel engine and optimal timing setup for its injection pump. The influence of biodiesel is studied by running experiments on an NA diesel bus engine MAN D2 2566 with a direct-injection M system. The fuel used is biodiesel produced from rapeseed. Special attention is focused on the determination of the optimal injection-pump timing with respect to engine harmful emissions, engine fuel consumption, and other engine performance parameters. These engine characteristics are compared against those obtained using conventional D2 diesel. Experiments with biodiesel and D2 are run on several engine operating regimes. The engine was monitored for possible operation problems and carefully examined after the tests. The results obtained are presented and analyzed. It is shown that with carefully optimized timing of the pump, the harmful emission of NOx, smoke, HC, and CO can be reduced essentially by keeping other engine characteristics within acceptable limits.
Introduction Care of environment, increasing prices, and uncertainties concerning mineral fuel availability necessitate the search for alternative fuels. In the near future, biodiesel fuels such as ethyl or methyl esters from soybean oil, rapeseed oil, sunflower oil, etc., offer a potentially very interesting alternative with respect to harmful emissions, engine wear, cost, and availability.1,2 Compared to mineral diesel, biodiesel fuels have comparable energy density and cetane number but have little sulfur and much oxygen. However, the high viscosity, high molecular weight, low volatility, etc., of biodiesel fuels may in some cases lead to problems, such as severe engine deposits, injector cooking, and piston ring sticking. At this time, most working diesel engines have been developed for operation with mineral diesel fuels. For these engines, biodiesel fuels can obviously not be used without any precautions. For this reason, many investigations are necessary to prevent or at least mitigate different engine or environmental problems. Compared to mineral diesel, biodiesel and biodiesel blends in general show lower CO, smoke, and HC emissions but higher NOx emission and higher specific fuel consumption.2-6 Using waste olive oil methyl ester as biodiesel may increase the NO2 * E-mail:
[email protected]. (1) Dorado, M. P.; Ballesteros, E.; Arnal, J. M.; Gomez, J.; Lopez, F. J. Fuel 2003, 82, 1311-1315. (2) Senda, J.; Okui, N.; Tsukamoto, T.; Fujimoto, H. On Board Measurement of Engine Performance and Emissions in Diesel Vehicle Operated with Biodiesel Fuel, SAE 2004 World Congress & Exhibition, Detroit, MI, March 2004; SAE Paper No. 2004-01-0083. (3) Nabi, N.; Akhter, S.; Shahadat, M. Z. Bioresour. Technol. 2006, 97, 372-378. (4) Alam, M.; Song, J.; Acharya, R.; Boehman, A.; Miller, K. Combustion and Emissions Performance of Low Sulfur, Ultralow Sulfur and Biodiesel Blends in a DI Diesel Engine, 2004 Powertrain & Fluid Systems Conference & Exhibition, Tampa, FL, Oct 2004; Paper No. 2004-01-3024. (5) Porai, P. T.; Chandrasekaran, S.; Subramaniyam, S.; Jancirani, J.; Sahoo, B. B. Combustion and Performance of a Diesel Engine with Oxygenated Diesel Blend, SAE 2004 World Congress & Exhibition, Detroit, MI, March 2004; Paper No. 2004-01-0082.
emissions up to 81%; the emissions of CO, NO, and SO2 may decrease, whereas the combustion efficiency remains constant using either biodiesel or mineral diesel.7 Several researchers have reported an inadvertent advance in fuel-injection timing, because biodiesel has a higher bulk modulus than mineral diesel.8-10 A higher bulk modulus, and therefore higher sound velocity, causes the pressure waves from the fuel pump to the hydraulically opened fuel injector to travel faster, thus advancing the fuel-injection timing. As well as inadvertent advance injection timing, an increase in the amount of fuel consumed during the premixed phase of combustion leads to increased NOx emissions. An opposite trend is observed with paraffinic fuels; this leads to a retarded injection timing because they have a lower bulk modulus of compressibility than mineral diesel and supports the observation that paraffinic fuels such as Fischer-Tropsch yield lower NOx emissions. In some cases, biodiesel showed an improved engine performance with lower emissions. Thus, biodiesel could potentially meet future emission norms by tuning the engine optimally for these fuels and by using appropriate exhaust posttreatment technology to offset the disadvantage of higher HC and NOx emission values, without any change in engine hardware.11 Another way to reduce NOx slightly is to apply EGR 3. (6) Senatore, A.; Cardone, M.; Rocco, V.; Prati, M. V. A ComparatiVe Analysis of Combustion Process in DI Diesel Engine Fueled with Biodiesel and Diesel Fuel, SAE 2000 World Congress, Detroit, MI, March 2000; Paper No. 2000-01-0691. (7) Dorado, M. P.; Ballesteros, E.; Arnal, J. M.; Gomez, J.; Lopez Gimenez, F. J. TEnergy Fuels 2003, 17, 1560-1565. (8) Nabi, N.; Shahadat, M. Z.; Rahman, S.; Beg, R. A.; BehaVior of Diesel Combustion and Exhaust Emission with Neat Diesel Fuel and DieselBiodiesel Blends, 2004 Powertrain & Fluid Systems Conference & Exhibition, Tampa, FL, Oct 2004; Paper No. 2004-01-3034. (9) Boehman, A.; Alam, M.; Song, J.; Acharya, R.; Szybist, J.; Zello, V.; Miller, K. Fuel Formulation Effects on Diesel Fuel Injection, Combustion, Emissions and Emission Control, Proceedings of DOE Diesel Engine Emissions Reductions Conference, Newport, RI, Aug 24-28, 2003. (10) Szybist, J.; Simmons, J.; Druckenmiller, M.; Al-Qurashi, K.; Boehman, A.; Scaroni, A. Potential Methods for NOx Reduction from Biodiesel, SAE Powertrain & Fluid Systems Conference & Exhibition, Pittsburgh, PA, Oct 2003; SAE Paper No. 2003-01-3205.
10.1021/ef050405a CCC: $33.50 © 2006 American Chemical Society Published on Web 05/03/2006
Optimal Timing of Diesel Engine Injection Pump
The effects of biodiesel fuels on transient emissions from modern diesel engines have also been investigated. The use of biodiesel resulted in lower emissions of HC, CO, and PM, with some increase in emissions of NOx on some engines.12 The results varied slightly, depending on the employed engine. The effect of biodiesel oxidation on engine performance and emissions at a single engine speed by three different injection timings has shown that the neat biodiesel from soybean and biodiesel blends produced NOx emissions 13-14% higher than mineral diesel; meanwhile, CO, HC, and smoke emission decreased.13 This paper presents the determination of optimal injection timing that reduces harmful emission, even NOx, of a bus diesel engine with an M injection system. The layout of the paper is as follows: at first, the influence of injection timing on engine characteristics is discussed. Attention is focused on those parameters that have been taken into account to determine the optimal injection-pump timing when using neat biodiesel. Both fuels, neat D2 diesel and neat biodiesel, are then compared with the injection timing, prescribed by the engine producer (for D2 diesel). Afterward, the effect of injection-pump timing for neat biodiesel is investigated. On the basis of the obtained results, we determined the optimal injection-pump timing for biodiesel. Injection-Pump Timing It is well-known that injection timing or start of injection is a very important parameter that significantly influences all engine characteristics.14,15 This is mainly due to the fact that injection timing influences the mixing quality of the air-fuel mixture and, consequently, the combustion process, including harmful emissions. It is generally known that retarded injection decreases maximal pressure in the cylinder and leads to a lower peak rate of heat transfer and consequently to lower combustion noise. Because the delayed injection leads to lower temperatures, the NOx emissions are also reduced. On the other hand, retarded injection leads to an increase in fuel consumption. Smoke emission may also increase, though trends vary significantly between different types and design of engines. For a directinjection diesel engine at high load, HC emissions are low and vary only modestly with injection timing. At partial loads, HC emissions are higher and increase as the injection start is shifted significantly from the optimum. This trend is especially evident at idle. Unfortunately, in mechanically controlled injection systems, the start of injection can hardly be controlled directly, because it depends on sophisticated transport phenomena in the pump, high-pressure tubes, and the injector. However, the start of injection is closely related to the start of injection-pump delivery, which can be set easily to any desired value. In this paper, the start of injection-pump delivery will be the primary variable parameter and throughout the paper, it will be called the injection-pump timing. (11) Sinha, S.; Agarwal, A. K. Performance EValuation of a BiodieselFueled Transport Diesel Engine, SAE 2005 World Congress & Exhibition, Detroit, MI, April 11-14, 2005; Paper No. 2005-01-1730. (12) Sharp, C. A.; Howell, S. A.; Jobe, J. The Effect of Biodiesel Fuels on Transient Emissions from Modern Diesel Engines, Part I Regulated Emissions and Performance, CEC/SAE Spring Fuels & Lubricants Meeting & Exposition, Paris, June 2000; SAE Paper No. 2000-01-1967. (13) Monyem, A.; van Gerpen, J. H. Biomass Bioenergy 2001, 20, 317325. (14) Bauer, H. Diesel-Engine Management; Robert Bosch: Stuttgart, Germany, 1999. (15) Stone, R. Introduction to Internal Combustion Engines; Palgrave MacMillan: Hampshire, U.K., 1995.
Energy & Fuels, Vol. 20, No. 4, 2006 1461 Table 1. Test Engine Main Specifications engine model engine type injection fuel-injection pump displacement compression ratio bore and stroke maximum power
MAN D 2566 MUM 4 stroke, 6 cylinder in line, water-cooled direct injection system with wall distribution (M system) Bosch PES 6A 95D 410 LS 2542 11 413 cm3 17.5:1 125 mm × 155 mm 162 kW at 2200 rpm
Table 2. Biodiesel and Diesel Properties density @ 30 °C (kg/m3) kinematic viscosity @ 30 °C (mm2/s) surface tension @ 30 °C (N/m) sound of velocity @ 20 °C, 100 bar (m/s) calorific value (J/kg) cetane number
D2
B100
827.4 3.34 0.0255 1347.6 43800 45-55
878.4 5.51 0.028 1383.6 38177 51
Table 3. Biodiesel Analysis ester content (% m/m) sulfur content (mg/kg) carbon residue on 10% distillation residue (% m/m) water content (mg/kg) oxidation stability, 100 °C (hours) acid value (mg of KOH/g) iodine value (g of I2/100 g) linolenic acid methyl ester (% m/m) methanol content (% m/m)
96.9
