PRELIMINARY INVESTIGATION OF DIESEL ENGINE WITH ADDITIONAL INJECTION OF ETHYL ALCOHOL

Transcription

1 Journal of KONES Internal Combustion Engines 2002 No. 3 4 ISSN PRELIMINARY INVESTIGATION OF DIESEL ENGINE WITH ADDITIONAL INJECTION OF ETHYL ALCOHOL Andrzej Kowalewicz, Grzegorz Pawlak Technical University of Radom Al. Chrobrego 45, Radom tel. (48) , fax (48) kowala@kiux.man.radom.pl Zbigniew Pajączek Scania Polska S.A. Stara Wieś k/nadarzyna Al. Katowicka 316, Nadarzyn tel. (22) , fax (22) zbigniew.pajaczek@scania.pl Abstract The objective of the work was investigation of possibility of dual fuelling of CI engine with diesel fuel and ethyl alcohol in order to decrease engine emission and increase its thermal efficiency. Alcohol, which is injected to the engine inlet port evaporates quickly, but doesn't ignite (due to low cetane number). After self-ignition of diesel fuel, ignited alcohol would promote further burning of it, that results in shorter combustion period, and thanks to that - increasing of thermal efficiency of the engine. Furthermore, later injection of diesel fuel would result in increasing of indicated work and decreasing of NO x. Preliminary investigation, which was carried out with the use of 1HC102 CI engine with modified inlet duct for injection of ethyl alcohol, showed that at the same torque and speed: thermal efficiency increased, engine torque increased, emission of HC and soot decreased, emission of greenhouse gas (CO 2 ) decreased, emission of NO x increased (beginning of diesel fuel injection was set up by the producer). Pressure histories measured during investigation were the base for computation of parameters which describe combustion process. For calculation were utilised computer programmes worked out in Department of IC Engines and Automobiles of Technical University of Radom. The results showed that there is influence if injected ethyl alcohol on engine operation, particularly it was noticed that the rate of fuel burning and heat release were higher. Introduction Ethyl alcohol is renewable fuel which could be applied in Poland on larger scale. There are many adventages of application of ethanol because it is enviromental friendly fuel as well as it could give a lot of economical beneficts. From the physical point of view it is also very good, because its evaporation rate and burning rate are very high and combustion is relatively clean. Application of ethyl alcohol as a fuel to SI engines doesn't meet any serious trouble. However, its application to CI engines meets some difficulties, concerned mainly with resistance to self ignition, due to very low cetane number. Other shortcoming are as follows: poor lubrication properties resulting from low viscosity and degradation of lubricating oil properties, corrosion and chemical degradation of engine materials, 136

2 poor miscibility with diesel fuel in presence of water. Physico-chemical properties of ethyl alcohol (Table l) and CI engine design, esspecially its fuel system, make impossible its direct application to CI engine. Physico-chemical properties of diesel fuel and ethanol [1], [2] Table 1 Property Diesel fuel Ethanol Density at 20, kg/m Calorific value, MJ/kg ~42,5 26,8 Calorific value of stechiometric mixture, MJ/ m 3 3,66-3,83 3,85 Heat of evaporation, kj/kg Temperature of selfignition, K ~ Stechiometric air/fuel ratio, kg air/ kg fuel 14,5 9,06 Lower flammability limit λ 0,98 2,06 Viscosity, cp 3,3-4,2 2,06 Octane number: - motored - research ~ Cetane number ,0 Flame temperature, K 2235 However it is possible to fuel the engine as a dual fuel one [3, 4] or with diesel fuel with small addition of alcohol (say up to 5 %) [5]. Because fuelling of the engine offers some possibilities of the control of the ratio of diesel fuel to ethanol, fuelling of CI seems to be interesting and promissing solution. The idea of dual fuel engine Main problem of diesel combustion is its ignition delay, which enable diesel engine to be run at a high speed. Local mixture formation, self-ignition and combustion needs time to be completed. Not-complete combustion of diesel fuel is a source of hydrocarbon emission and smoke. In order to avoid this unconvenient effect, injection of ethanol to inlet duct is considered. Ethanol will quickly evaporate (but will not self-ignite) before self-ignition of diesel fuel droplet, and then will be ignited by burning droplets, resulting in very high combustion rate of both fuels, especially diesel fuel. Thanks higher combustion rate it may be expected: higher thermal efficiency, higher power output, lower emission of HC and soot. The present research work was based on the idea of dual-fuelling of CI engine with diesel fuel and ethanol. Ethanol is injected additionally, independently to diesel fuel. It is injected into the inlet manifold with the use of additional injector installed in it. The dose of alcohol are limited up to 40% of total energy which is provided to the engine with diesel fuel and alcohol together. This assumtion would also prevent the engine from knocking. The objectives of the work are as follows: testing of the possibility of application ethyl alcohol to CI engine according to the authors idea, validation of the expected increase of engine output and decrease of emission 137

3 optimisation of the ratio of energy of both fuels, optimisation of the beginning of injection of diesel fuel. Engine test stand For experiment a test stand shown in Fig. 1. was prepared. Main part of it is one-cylinder 1HC102 CI engine. Fig.1. Test stand Engine torque was measured by means of an electric dynamometer Vibrometer 3WB15. Diesel-fuel consumption and ethanol consumption were measured with the use of automatic dose meters PG 80. Air flow was measured with the use of a flow-meter installed on the air tank which reduced pressure pulsations. In order to analyse combustion proccess some measurement of pressure inside combustion chamber was done. Pressure transducer AVL 8QP 505 ca. was inserted in the cylinder head for measuring the pressure-time history in the cylinder with the use of high speed measurement system worked out in Department of Internal Combustion Engine and Automobile [6]. For exhaust gas analysis, esspecially for CO, CO 2, HC, AVL DiGas 465 analyser was used. NO x emission was measured by Beckman Analyser Model 951. Investigations Investigations were carried out for constant speed and varying load. Measurement points were choosen in such a way, that the comparison of engine parameters and emission could be obtained for the same load but for different proportion of the diesel fuel to ethanol. For comparison of both fuelling systems (i.e. standard and dual fuelling), investigation were carried out in the case when the engine was fuelled with diesel-fuel only. The following engine parameters were measured: 138

4 engine torque and speed, fuel consumption for both fuels (i.e. ethanol and diesel fuel), air consumption, emissions (NO x, CO, CO 2, HC) and opacity of exhaust gases, cylinder pressure vs crank angle. Results and discussion Performance Fig. 2 shows how engine overall efficiency is affected by additional ethanol injection. It enables to compare the efficiency for different engine load and different diesel fuel ethanol ratio for the same engine speed No ethanol 2 - Ethanol dose energy d1= kj/cycle 3 - Ethanol dose energy d2= kj/cycle 4 - Ethanol dose energy d3= kj/cycle engine overall efficiency [-] Torque [Nm] Fig. 2. Engine overall efficiency vs. engine torque for three ethanol doses and different load increased by increasing dose of diesel fuel for n = 1800 rpm. As it may be seen engine overall efficiency rises when ethanol dose is increased. Engine overall efficiency is η o = 0,285 for the engine fuelled with neat diesel fuel and engine torque is T = 36 Nm. Engine overall efficiency increased up to η o = 0,305 and torque to 51 Nm for fuellling the engine with the same diesel fuel dose and injection of higher and higher ethanol dose. Increasing of ethanol share in the total fuel energy causes the rise of load as well as the rise of engine overall efficiency (Fig. 3). 139

5 Diesel fuel dose ON1=1.174 kj/cycle Diesel fuel dose ON2=1.517 kj/cycle Diesel fuel dose ON3=1.789 kj/cycle engine overall efficiency [-] Ethanol dose energy / diesel fuel dose energy [-] Fig. 3. Engine overall efficiency vs. ethanol to diesel fuel dose energy ratio and different load increased by increasing dose of ethanol for n = 1800 rpm. For the same fuel energy for torque T > 45 Nm (i.e. total fuel energy per cycle 2 kg/cycle) higher torque may be obtained for dual fuelling than for diesel fuel operation only, Fig Torque [Nm] Diesel fuel only - load as below (ON1) Diesel fuel dose (ON1) 1,174 kj/cycle + Ethanol Diesel fuel only - load as below (ON3) Diesel fuel dose (ON3) 1,517 kj/cycle + Ethanol Diesel fuel only - load as below (ON2) Diesel fuel dose (ON2) 1,789 kj/cycle + Ethanol Total fuel energy per cycle [kj/cycle] Fig. 4. Torque vs. total fuel energy per cycle, n = 1800 rpm. 140

6 Emissions Hydrocarbons emission measured is shown in fig. 5. It is lower for dual fuelling in wide range of ethanol energy to diesel fuel energy pure diesel fuel (T3=41 Nm) Ethanol dose d1= kj/cycle Ethanol dose d2= kj/cycle Ethanol dose d3= kj/cycle pure diesel fuel (T2=36,8 Nm) 3 - diesel fuel + ethanol (T3=41 Nm) HC emission [ppm] diesel fuel + ethanol (T2=36,8 Nm) 1- diesel fuel + ethanol (T1=26,5 Nm) pure diesel fuel (T1=26,5 Nm) ethanol energy/ diesel oil energy [-] Fig. 5. HC emission vs. ethanol dose energy to diesel fuel dose energy ratio for n = 1800 rpm. Carbon monoxide emission is shown in fig. 6. As far as CO is concerned there were no significat changes in comparisson with standard fuelling. Eg. CO emission was 0,2% for engine load T = 36,5 Nm for standard fuelling and it also was 0,2% for the same load obtained when the engine was fuelled with diesel fuel and ethanol Diesel fuel dose ON1=1,174 kj/cycle + Ethanol Diesel fuel dose ON3=1,517 kj/cycle + Ethanol Diesel fuel dose ON2=1,789 kj/cycle + Ethanol Only diesel fuel - load as for ON1 + Ethanol Only diesel fuel - load as for ON2 + Ethanol Only diesel fuel - load as for ON3 + Ethanol Emission CO [% vol.] Total fuel energy per cycle [kj/cycle] Fig. 6. Carbon monoxide emission vs. total fuel energy per cycle, n = 1800 rpm. Smoke level is lower for dual fuelling. Preliminary measurement of NO x emission shows that for dual fuel engine it is 20% higher than for standard fuelling. 141

7 Maximum pressure in the cylinder is higher for dual-fuelling than for standard fuelling. Combustion time of dual-fuelling is shorter than for standard fuelling. Presented results comes from preliminary engine tests. They show that there is possiblity for efficient fuelling of CI engine with diesel fuel with additional dose of ethanol. Next tests should include also examination of the engine control. Conclusion Dual fuelling, i.e. with diesel fuel and ethanol in comparison with standard fuelling, i.e. with diesel fuel only, is more efficient and more friendly for environment (except of nitric-oxide emission, which may be reduced by the use of selective catalyst). Higher overall efficiency is caused by improvement of combustion processes; lower hydrocarbon emission and partly carbon-monoxide emission. Higher nitric-oxide emission also validate this proposal. Above mentioned results are very promising and should be continued. References 1. Kowalewicz A.: Podstawy procesów spalania. WNT, Warszawa Kowalewicz A.: Wybrane zagadnienia silników spalinowych. Wydawnictwo WSI Radom, Radom Kowalewicz A.: Methanol as a Fuel for CI Engines. A review and Analysis. Proceedings of the International Symposium on Small Diesel Engines Warsaw 92, International Council of Combustion Engines CIMAC, Kowalewicz A., Luft S.: Analysis of Combustion in Compression Ignition Engine Fuelled with Methanol Vapour. Archiwum Combustionis, vol. 14 (1994), No Ethanol Busses Strenghten Image. Scania World, April Różycki A.: System pomiarowy wielkości szybkozmiennych w zastosowaniu do badań silnikowych. Silniki Spalinowe Nr 115. Wydawnictwo HCP Ciegielski, Poznań