Eco-diesel engine fuelled with rapeseed oil methyl ester ...web.mit.edu/nuwong/Public/Diesohol/Kowalewicz_Eco... · (c) decreases with an increasein V E for any injection (b) is comparable

1275

Eco-diesel engine fuelled with rapeseed oil methyl esterand ethanol. Part 2: comparison of emissions andefficiency for two base fuels: diesel fuel and esterA KowalewiczTechnical University of Radom, ul. Chrobrego 45, Radom, 26-600, Poland. email: [email protected]

The manuscript was received on 21 November 2005 and was accepted after revision for publication on 12 May 2006.

DOI: 10.1243/09544070JAUTO218

Abstract: A comparison has been made of the efficiency and emissions from a single-cylindernaturally aspirated direct injection compression ignition engine when fuelled either with dieselfuel (DF) or rapeseed oil methyl ester (RME) and additionally with ethanol in different pro-portions injected into the inlet port during the suction stroke. Investigations were performedat two constant loads, high and low. At each load the proportions of ethanol and base fuelwere changed in such a way that the load was held constant. At each load the engine operatedat a constant speed and for three injection timings. The obtained results were similar for bothfuels, but in the case of RME there were lower carbon dioxide and smoke emissions and insome operating conditions NO

xemission was observed. The aim of the ethanol injection, which

was produced with air premixed with a homogeneous mixture in the cylinder, was to promoteand accelerate combustion of DF/RME droplets, resulting in shorter combustion of the totalfuel. The second objective of ethanol addition was to decrease the emissions of smoke andcarbon dioxide, because as ethanol burns its combustion products have more H

2O and less

CO2. 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 25 per cent for RMEand about 20 per cent for diesel fuel.

Keywords: rapeseed oil methyl ester (RME), ethanol, diesel fuel, emission, engine efficiency

1 INTRODUCTION methyl ester (RME) and additionally with ethanolinjected into the inlet port. Experiments were carriedout in the same way and with the use of the sameIn the first part of the paper on efficiency anddirect injection (DI) CI engine, measuring equip-emission [1] a novel approach of fuelling with rape-ment, and test stand as presented in the first part ofseed oil methyl ester (RME) together with ethanolthe paper. The test procedure was also the same. Theinjected into the inlet port during the suction strokephysicochemical properties of the fuels used arehas been described and brake fuel conversion

efficiency and emissions as a function of the shown in Table 1.The investigation was carried out at a constantenergetic fraction of ethanol in the total fuel, V

E,

have been analysed. In the third part of the paper speed of 1800 r/min at two loads: 20 and 40 N m. Ateach load the three injection timings of the base fuel[2] combustion characteristics (ignition delay, com-

bustion time, pressure in the cylinder, heat release at 25, 30 and 35° BTDC (before top dead centre) wereapplied. Measurement points were chosen in suchrate, and fraction of fuel burnt versus crank angle,

CA) will be shown and analysed. In this paper a a way that a comparison of the engine parametersand emissions could be obtained for the same loadcomparison has been made of the emissions and

efficiency of a compression ignition (CI) engine but for different proportions of ethanol to base fuel(DF or RME).fuelled with either diesel fuel (DF) or rapeseed oil

JAUTO218 © IMechE 2006 Proc. IMechE Vol. 220 Part D: J. Automobile Engineering

1276 A Kowalewicz

Table 1 Physicochemical properties of diesel fuel, RME, and ethanol

Property DF RME Ethanol

Chemical formula — — C2H

5OH

Molecular weight (g/mol) ~170 — 46Density at 20 °C (kg/m3) 838 878 789Calorific value (MJ/kg) 41.03 38.5 26.9Calorific value of stoichiometric mixture (MJ/m3) — — 3.85Heat of evaporation (kJ/kg) 270 250 840Temperature of self-ignition (K) ~500 ~400 665Stoichiometric air/fuel ratio (kg air/kg fuel) 14.5 13.6 9.0Lower flammability l

l0.98 — 2.06

Higher flammability lh

0.19 — 0.30Kinematic viscosity at 40 °C (mm2/s) 2.97 4.58 1.4Motor octane number (MON)/research octane number (RON) — — 89/107Cetane number 58 60 8Flame temperature (K) — — 2235Molecular composition (by mass)

C 0.870 0.775 0.522H 0.130 0.121 0.130O — 0.104 0.348

2 RESULTS AND DISCUSSION (d) VE>0.20 for DF fuel and V

E>0.25 for RME and

does not influence emissions.2.1 Emissions

Explanations of these results are as follows. RME hasThe best results with regard to emissions were less carbon in its molecules than DF and so has aobtained for carbon dioxide and smoke. For example, lower CO

2emission. A decrease in CO

2emission is a

the emissions of carbon dioxide for two base fuels result of higher VE

. The products of ethanol com-versus V

Eare shown in Figs 1 and 2. From these bustion contain less CO

2and more H

2O. A higher

and other measurements it can be stated that CO2

CO2

emission is a result of more fuel burnt at aemission: higher load.

Smoke emissions are shown in Figs 3 and 4. It can(a) is a little lower for fuelling with RME in com- be stated that smoke emission:

parison with the engine fuelled with DF;(b) is higher at high load than at low load for any V

E(a) is lower for fuelling with RME at any load in com-

parison with the engine fuelled with DF;for both DF and RME;(c) decreases with an increase inV

Efor any injection (b) is higher at high load than at low load for any V

Efor both DF and RME;timing for both DF and RME;

Fig. 1 Comparison of carbon dioxide emission versus VE

at low load for engine fuelling withdiesel fuel and ethanol and RME and ethanol

JAUTO218 © IMechE 2006Proc. IMechE Vol. 220 Part D: J. Automobile Engineering

1277Eco-diesel engine fuelled with rapeseed oil methyl ester and ethanol. Part 2

Fig. 2 Comparison of carbon dioxide emission versus VE

at high load for engine fuelling withdiesel fuel and ethanol and RME and ethanol

Fig. 3 Comparison of smoke emission versus VE

at low load for engine fuelling with diesel fueland ethanol and RME and ethanol

Fig. 4 Comparison of smoke emission versus VE

at high load for engine fuelling with diesel fueland ethanol and RME and ethanol


1278 A Kowalewicz

(c) decreases with an increase inVE

for any injection (b) is comparable for both fuels, excluding the casetiming and at any load for both DF and RME; of high load and early injection (35° CA BTDC)

(d) VE>0.20 for DF fuel and V

E>0.25 for RME and when it is higher;

does not influence emissions; (c) at low load decreases with an increase in ethanol(e) is highest for fuelling with neat DF or RME. addition for both fuels (DF and RME) and for all

injection timings;Lower smoke emissions for fuelling with RME result

(d) at high load and for early injection (a= 35° CAfrom the fact that RME is an oxygenated fuel (withBTDC) increases with ethanol addition for both34.8 per cent by mass of oxygen in the molecule).fuels;At high loads smoke emission is always higher than

(e) for middle and early injection increases veryat low loads. The addition of ethanol increases thelittle with ethanol addition for DF and is ratherfraction in a homogeneous ethanol–air gaseousconstant for RME fuel;mixture, which burns without smoke.

(f) for the same injection timing increases with load;A comparison of nitrogen oxides emissions is(g) increases for the earlier injection at any speedshown in Figs 5 and 6. It can be stated that NO

x and load for both fuels.emission:

An explanation of these facts is as follows. Lower(a) is lower for fuelling with RME at low load and anyV

Eand injection timing in comparison with DF; NO

xemissions for fuelling with RME are a result of

Fig. 5 Comparison of nitrogen oxides emission versus VE


Fig. 6 Comparison of nitrogen oxides emission versus VE




a lower temperature level of the cycle due to a lower is shifted towards the expansion stroke. A highNO

xemission at both loads is a result of the highercalorific value of RME. However, at high load and for

early injection the influence of ethanol addition is temperature level of the cycle.A comparison of carbon monoxide emissions isstronger for the oxygenated fuel, RME, than for DF.

A decrease in NOx

emission with an increase in shown in Figs 7 and 8. It can be stated that COemission:ethanol addition at low load is a result of the cooling

effect of ethanol evaporation. For example, the tem-perature drop at the inlet for V

E=0.25 reaches about (a) is comparable for both DF and RME in the whole

range of the experiment;10–17 °C while the exhaust gas temperature is verylow at about 220–290 °C (depending on the injection (b) is comparable for both loads, low and high;

(c) increases with an increase in ethanol addition fortiming). For high load and early injection of RME,however, this effect is dominated by faster com- both fuels, both loads, and for all injection

timings;bustion, resulting in an increase in temperatureand more heat being evolved in the cylinder. For (d) increases more quickly for RME than for DF with

increasing VE

.high load, the exhaust gas temperature is almostindependent of the ethanol fraction and is at a levelof 380–420 °C, depending on the injection timing. An explanation of these facts is as follows. CO

emission is influenced by the same conditions forThis is visible for early injection, while for middleand late injection timing the NO

xemission decreases both fuels. Ethanol addition results in a lower tem-

perature level and hence higher CO emission.due to the lower temperature of combustion, which

Fig. 7 Comparison of carbon monoxide emission versus VE


Fig. 8 Comparison of carbon monoxide emission versus VE



1280 A Kowalewicz

A comparison of HC emissions is shown in Figs 9 values of both fuels. The b.f.c.e. depends strongly onand 10. It can be stated that HC emission: load and speed; other parameters have only a slight

influence on it (Figs 11 and 12). From these and other(a) is higher for RME than for DF at higher load;

results (not shown in the paper) it may be stated that:(b) at low load is comparable for both RME and DF;(c) V

E=0.20 is optimum for DF fuel and V

E>0.25

(a) b.f.c.e. is higher for fuelling with DF than withfor RME and does not influence HC emissions.RME for V

E<0.4;

This fact may be explained as follows. The lower (b) in general, the higher the load, the higher thecalorific value of RME results in a lower temperature b.f.c.e. for both DF and RME;level and in consequence worse combustion. This (c) the influence of ethanol addition on b.f.c.e. isinfluence is higher, the higher the fraction of ethanol not very strong, with the exception of engineapplied. operation with DF at high load, when it increases

with an increase of ethanol addition;2.2 Brake fuel conversion efficiency (d) V

E>0.20 for DF fuel and does not influence

b.f.c.e. at high load;Brake fuel conversion efficiency (b.f.c.e.) was com-(e) the highest efficiency appears at the middleputed at each point in the experiment by measuring

fuel consumption, engine speed, load, and calorific injection timing.

Fig. 9 Comparison of hydrocarbon emission versus VE

at low load for engine fuelling with dieselfuel and ethanol and RME and ethanol

Fig. 10 Comparison of hydrocarbon emission versus VE




Fig. 11 Comparison of brake fuel conversion efficiency versus VE

at low load for engine fuellingwith diesel fuel and ethanol and RME and ethanol

Fig. 12 Comparison of brake fuel conversion efficiency versus VE

at high load for engine fuellingwith diesel fuel and ethanol and RME and ethanol

The first two results are clear: the higher efficiency 1. Injection of ethanol into the inlet port reducesCO

2emission, smoke, and – in the case of lowfor DF results in a higher temperature, which assists

the higher calorific value of this fuel and the high load – NOx

emission for fuelling both with DFand RME.load. The positive influence of ethanol is visible only

in the range of very low b.f.c.e. at high load, which 2. It is more advantageous to fuel the engine withrapeseed oil methyl ester as a base fuel than withpromotes burning of DF fuel in the case where com-

bustion of the big mass of DF is not efficient due diesel fuel on account of the lower emissions ofCO

2, smoke, and in some operating conditionsto the time being too short for completion (RME

is an oxygenated fuel and its combustion time is NOx.

3. The ethanol fraction in the total fuel (i.e. the baseshorter [2]). The last statement follows from the factthat middle injection timing is optimum from the fuel and ethanol itself) at low load may reach

50 per cent and at high load 30 per cent but ispoint of view of combustion (maximum heat releaserate localization with respect to top dead centre, limited by diesel knock.

4. The optimum injection timing of DF and RME onor TDC).account of minimum NO

xemissions seems to be

delayed injection (25° CA BTDC) and on accountof efficiency early injection (30° CA BTDC).3 CONCLUSIONS

5. The sufficient effective ratio of ethanol energy VE

to total fuel energy for DF is 20 per cent andFrom the experiment the following conclusions maybe drawn: for RME is 25 per cent (by mass 37.6 and 33 per


1282 A Kowalewicz

CA crank anglecent respectively) and higher values of VE

do notinfluence emissions and b.f.c.e. CI compression ignition

DF diesel fuelDI CI direct injection compression ignitionRME rapeseed oil methyl esterREFERENCES

1 Kowalewicz, A. Eco-diesel engine fuelled with rape-seed oil methyl ester and ethanol. Part 1: efficiency APPENDIX 2and emission. Proc. IMechE, Part D: J. AutomobileEngineering, 2005, 219(D5), 715–723. Mass and the volumetric proportion of ethanol to

2 Kowalewicz, A. Eco-diesel engine fuelled with rape- RME versus ethanol energy to total fuel energy VEseed oil methyl ester and ethanol. Part 3: com-

are shown in Table 2, wherebustion processes. Proc. IMechE, Part D: J. AutomobileEngineering, 2006, 220(D9), 1283–1291 (this issue). mE=mass ethanol flow

mRME=mass RME flow

APPENDIX 1Table 2 Values of energy and

mass ratio*Notation

VE

mE

mRME

mE

mDF

n engine speed (r/min)T engine torque (N m)

0.05 0.084 0.089VE

ratio of ethanol energy to energy of the0.1 0.177 0.189

total fuel (DF or RME and ethanol) 0.2 0.399 0.4250.3 0.684 0.7280.4 1.063 1.133Abbreviations0.5 1.595 1.700

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


Documents

Eco-diesel engine fuelled with rapeseed oil methyl ester ...web.mit.edu/nuwong/Public/Diesohol/Kowalewicz_Eco... · (c) decreases with an increasein V E for any injection (b) is comparable