A Kowalewicz Technical University of Radom, ul. Chrobrego 45, Radom, , Poland.

Transcription

1 co-diesel engine fuelled with rapeseed oil methyl ester and ethanol. Part : comparison of emissions and efficiency for two base fuels: diesel fuel and ester A Kowalewicz Technical University of Radom, ul. Chrobrego 45, Radom, 6-600, Poland. andrzej.kowalewicz@pr.radom.pl The manuscript was received on 1 November 005 and was accepted after revision for publication on 1 May 006. DOI: / JAUTO Abstract: A comparison has been made of the efficiency and emissions from a single-cylinder naturally aspirated direct injection compression ignition engine when fuelled either with diesel fuel (DF) or rapeseed oil methyl ester (RM) and additionally with ethanol in different proportions injected into the inlet port during the suction stroke. Investigations were performed at two constant loads, high and low. At each load the proportions of ethanol and base fuel were changed in such a way that the load was held constant. At each load the engine operated at a constant speed and for three injection timings. The obtained results were similar for both fuels, but in the case of RM there were lower carbon dioide and smoke emissions and in some operating conditions NO emission was observed. The aim of the ethanol injection, which was produced with air premied with a homogeneous miture in the cylinder, was to promote and accelerate combustion of DF/RM droplets, resulting in shorter combustion of the total fuel. The second objective of ethanol addition was to decrease the emissions of smoke and carbon dioide, because as ethanol burns its combustion products have more H O and less CO. The aim was to provide a sufficient effective energetic fraction of ethanol in order to reach a satisfactory decrease in emissions, which was found to be about 5 per cent for RM and about 0 per cent for diesel fuel. Keywords: rapeseed oil methyl ester (RM), ethanol, diesel fuel, emission, engine efficiency 1 INTRODUCTION methyl ester (RM) and additionally with ethanol injected into the inlet port. periments were carried In the first part of the paper on efficiency and out in the same way and with the use of the same emission [1] a novel approach of fuelling with rapement, direct injection (DI) CI engine, measuring equip- seed oil methyl ester (RM) together with ethanol and test stand as presented in the first part of injected into the inlet port during the suction stroke the paper. The test procedure was also the same. The has been described and brake fuel conversion physicochemical properties of the fuels used are efficiency and emissions as a function of the shown in Table 1. energetic fraction of ethanol in the total fuel, V, The investigation was carried out at a constant have been analysed. In the third part of the paper speed of 1800 r/min at two loads: 0 and 40 N m. At [] combustion characteristics (ignition delay, combustion each load the three injection timings of the base fuel time, pressure in the cylinder, heat release at 5, 30 and 35 BTDC (before top dead centre) were rate, and fraction of fuel burnt versus crank angle, applied. Measurement points were chosen in such CA) will be shown and analysed. In this paper a a way that a comparison of the engine parameters comparison has been made of the emissions and and emissions could be obtained for the same load efficiency of a compression ignition (CI) engine but for different proportions of ethanol to base fuel fuelled with either diesel fuel (DF) or rapeseed oil (DF or RM). JAUTO18 IMech 006 Proc. IMech Vol. 0 Part D: J. Automobile ngineering

2 176 A Kowalewicz Table 1 Physicochemical properties of diesel fuel, RM, and ethanol Property DF RM thanol Chemical formula C H OH 5 Molecular weight (g/mol) ~ Density at 0 C (kg/m3) Calorific value (MJ/kg) Calorific value of stoichiometric miture (MJ/m3) 3.85 Heat of evaporation (kj/kg) Temperature of self-ignition (K) ~500 ~ Stoichiometric air/fuel ratio (kg air/kg fuel) Lower flammability l Higher flammability l h Kinematic viscosity at 40 C (mm/s) Motor octane number (MON)/research octane number (RON) 89/107 Cetane number Flame temperature (K) 35 Molecular composition (by mass) C H O RSULTS AND DISCUSSION (d) V >0.0 for DF fuel and V >0.5 for RM and does not influence emissions..1 missions planations of these results are as follows. RM has The best results with regard to emissions were less carbon in its molecules than DF and so has a obtained for carbon dioide and smoke. For eample, lower CO emission. A decrease in CO emission is a the emissions of carbon dioide for two base fuels result of higher V. The products of ethanol comversus V are shown in Figs 1 and. From these bustion contain less CO and more H O. A higher and other measurements it can be stated that CO CO emission is a result of more fuel burnt at a emission: higher load. Smoke emissions are shown in Figs 3 and 4. It can (a) is a little lower for fuelling with RM in combe stated that smoke emission: parison with the engine fuelled with DF; (b) is higher at high load than at low load for any V (a) is lower for fuelling with RM at any load in comparison with the engine fuelled with DF; for both DF and RM; (c) decreases with an increase in V for any injection (b) is higher at high load than at low load for any V timing for both DF and RM; for both DF and RM; Fig. 1 Comparison of carbon dioide emission versus V at low load for engine fuelling with diesel fuel and ethanol and RM and ethanol Proc. IMech Vol. 0 Part D: J. Automobile ngineering JAUTO18 IMech 006

3 co-diesel engine fuelled with rapeseed oil methyl ester and ethanol. Part 177 Fig. Comparison of carbon dioide emission versus V at high load for engine fuelling with diesel fuel and ethanol and RM and ethanol Fig. 3 Comparison of smoke emission versus V at low load for engine fuelling with diesel fuel and ethanol and RM and ethanol Fig. 4 Comparison of smoke emission versus V at high load for engine fuelling with diesel fuel and ethanol and RM and ethanol JAUTO18 IMech 006 Proc. IMech Vol. 0 Part D: J. Automobile ngineering

4 178 A Kowalewicz (c) decreases with an increase in V for any injection timing and at any load for both DF and RM; (d) V >0.0 for DF fuel and V >0.5 for RM and does not influence emissions; (e) is highest for fuelling with neat DF or RM. Lower smoke emissions for fuelling with RM result from the fact that RM is an oygenated fuel (with 34.8 per cent by mass of oygen in the molecule). At high loads smoke emission is always higher than at low loads. The addition of ethanol increases the fraction in a homogeneous ethanol air gaseous miture, which burns without smoke. A comparison of nitrogen oides emissions is shown in Figs 5 and 6. It can be stated that NO emission: (a) is lower for fuelling with RM at low load and any V and injection timing in comparison with DF; (b) is comparable for both fuels, ecluding the case of high load and early injection (35 CA BTDC) when it is higher; (c) at low load decreases with an increase in ethanol addition for both fuels (DF and RM) and for all injection timings; (d) at high load and for early injection (a= 35 CA BTDC) increases with ethanol addition for both fuels; (e) for middle and early injection increases very little with ethanol addition for DF and is rather constant for RM fuel; (f) for the same injection timing increases with load; (g) increases for the earlier injection at any speed and load for both fuels. An eplanation of these facts is as follows. Lower NO emissions for fuelling with RM are a result of Fig. 5 Comparison of nitrogen oides emission versus V at low load for engine fuelling with diesel fuel and ethanol and RM and ethanol Fig. 6 Comparison of nitrogen oides emission versus V at high load for engine fuelling with diesel fuel and ethanol and RM and ethanol Proc. IMech Vol. 0 Part D: J. Automobile ngineering JAUTO18 IMech 006

5 co-diesel engine fuelled with rapeseed oil methyl ester and ethanol. Part 179 a lower temperature level of the cycle due to a lower calorific value of RM. However, at high load and for early injection the influence of ethanol addition is stronger for the oygenated fuel, RM, than for DF. A decrease in NO emission with an increase in ethanol addition at low load is a result of the cooling effect of ethanol evaporation. For eample, the temperature drop at the inlet for V =0.5 reaches about C while the ehaust gas temperature is very low at about 0 90 C (depending on the injection timing). For high load and early injection of RM, however, this effect is dominated by faster combustion, resulting in an increase in temperature and more heat being evolved in the cylinder. For high load, the ehaust gas temperature is almost independent of the ethanol fraction and is at a level of C, depending on the injection timing. This is visible for early injection, while for middle and late injection timing the NO emission decreases due to the lower temperature of combustion, which is shifted towards the epansion stroke. A high NO emission at both loads is a result of the higher temperature level of the cycle. A comparison of carbon monoide emissions is shown in Figs 7 and 8. It can be stated that CO emission: (a) is comparable for both DF and RM in the whole range of the eperiment; (b) is comparable for both loads, low and high; (c) increases with an increase in ethanol addition for both fuels, both loads, and for all injection timings; (d) increases more quickly for RM than for DF with increasing V. An eplanation of these facts is as follows. CO emission is influenced by the same conditions for both fuels. thanol addition results in a lower temperature level and hence higher CO emission. Fig. 7 Comparison of carbon monoide emission versus V at low load for engine fuelling with diesel fuel and ethanol and RM and ethanol Fig. 8 Comparison of carbon monoide emission versus V at high load for engine fuelling with diesel fuel and ethanol and RM and ethanol JAUTO18 IMech 006 Proc. IMech Vol. 0 Part D: J. Automobile ngineering

6 180 A Kowalewicz A comparison of HC emissions is shown in Figs 9 and 10. It can be stated that HC emission: (a) is higher for RM than for DF at higher load; (b) at low load is comparable for both RM and DF; (c) V =0.0 is optimum for DF fuel and V >0.5 for RM and does not influence HC emissions. values of both fuels. The b.f.c.e. depends strongly on load and speed; other parameters have only a slight influence on it (Figs 11 and 1). From these and other results (not shown in the paper) it may be stated that: (a) b.f.c.e. is higher for fuelling with DF than with RM for V <0.4; This fact may be eplained as follows. The lower (b) in general, the higher the load, the higher the calorific value of RM results in a lower temperature b.f.c.e. for both DF and RM; level and in consequence worse combustion. This (c) the influence of ethanol addition on b.f.c.e. is influence is higher, the higher the fraction of ethanol not very strong, with the eception of engine applied. operation with DF at high load, when it increases with an increase of ethanol addition;. Brake fuel conversion efficiency (d) V >0.0 for DF fuel and does not influence Brake fuel conversion efficiency (b.f.c.e.) was com- b.f.c.e. at high load; puted at each point in the eperiment by measuring fuel consumption, engine speed, load, and calorific (e) the highest efficiency appears at the middle injection timing. Fig. 9 Comparison of hydrocarbon emission versus V at low load for engine fuelling with diesel fuel and ethanol and RM and ethanol Fig. 10 Comparison of hydrocarbon emission versus V at high load for engine fuelling with diesel fuel and ethanol and RM and ethanol Proc. IMech Vol. 0 Part D: J. Automobile ngineering JAUTO18 IMech 006

7 co-diesel engine fuelled with rapeseed oil methyl ester and ethanol. Part 181 Fig. 11 Comparison of brake fuel conversion efficiency versus V at low load for engine fuelling with diesel fuel and ethanol and RM and ethanol Fig. 1 Comparison of brake fuel conversion efficiency versus V at high load for engine fuelling with diesel fuel and ethanol and RM and ethanol The first two results are clear: the higher efficiency 1. Injection of ethanol into the inlet port reduces for DF results in a higher temperature, which assists CO emission, smoke, and in the case of low the higher calorific value of this fuel and the high load NO emission for fuelling both with DF load. The positive influence of ethanol is visible only and RM. in the range of very low b.f.c.e. at high load, which. It is more advantageous to fuel the engine with promotes burning of DF fuel in the case where combustion rapeseed oil methyl ester as a base fuel than with of the big mass of DF is not efficient due diesel fuel on account of the lower emissions of to the time being too short for completion (RM CO, smoke, and in some operating conditions is an oygenated fuel and its combustion time is NO. shorter []). The last statement follows from the fact 3. The ethanol fraction in the total fuel (i.e. the base that middle injection timing is optimum from the fuel and ethanol itself) at low load may reach point of view of combustion (maimum heat release 50 per cent and at high load 30 per cent but is rate localization with respect to top dead centre, limited by diesel knock. or TDC). 4. The optimum injection timing of DF and RM on 3 CONCLUSIONS account of minimum NO emissions seems to be delayed injection (5 CA BTDC) and on account of efficiency early injection (30 CA BTDC). 5. The sufficient effective ratio of ethanol energy V From the eperiment the following conclusions may to total fuel energy for DF is 0 per cent and be drawn: for RM is 5 per cent (by mass 37.6 and 33 per JAUTO18 IMech 006 Proc. IMech Vol. 0 Part D: J. Automobile ngineering

8 18 A Kowalewicz cent respectively) and higher values of V do not CA crank angle influence emissions and b.f.c.e. CI compression ignition DF diesel fuel DI CI direct injection compression ignition RFRNCS RM rapeseed oil methyl ester 1 Kowalewicz, A. co-diesel engine fuelled with rapeseed oil methyl ester and ethanol. Part 1: efficiency APPNDIX and emission. Proc. IMech, Part D: J. Automobile ngineering, 005, 19(D5), Mass and the volumetric proportion of ethanol to Kowalewicz, A. co-diesel engine fuelled with rape- RM versus ethanol energy to total fuel energy V seed oil methyl ester and ethanol. Part 3: com- bustion processes. Proc. IMech, Part D: J. Automobile are shown in Table, where ngineering, 006, 0(D9), (this issue). m =mass ethanol flow APPNDIX 1 Notation m RM =mass RM flow Table Values of energy and mass ratio* m m n engine speed (r/min) V m m T engine torque (N m) RM DF V ratio of ethanol energy to energy of the total fuel (DF or RM and ethanol) Abbreviations b.f.c.e. brake fuel conversion efficiency *It is taken into account that ethanol BTDC before top dead centre contains 8 per cent water by volume Proc. IMech Vol. 0 Part D: J. Automobile ngineering JAUTO18 IMech 006