07-02-2013, 03:50 PM
Diesel Emission Control by Hot EGR and Ethanol Fumigation; an Experimental Investigation
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ABSTRACT:
Exhaust Gas Recirculation has emerged as one of the promising technique in abating oxides of Nitrogen but combustion quality deteriorates at higher loads and higher percentage of Exhaust Gas Recirculation do not become attractive owing to decreased efficiency and increased hydrocarbon and smoke. Another technology that offers promise of being able to reduce engine emissions is alcohol fumigation. An experimental investigation is carried to examine the performance and emission with alcohol fumigation in the presence of hot Exhaust Gas Recirculation on a single cylinder DI diesel engine. The main focus was on oxides of nitrogen, hydrocarbon and smoke emission and variations in thermal efficiency. Results pertaining to Exhaust Gas Recirculation showed greater reductions in NOx emission. The reductions in the efficiency were marginal (about 5%) up to 30% Exhaust Gas Recirculation but tend to increase amounting up to 30 to 40% at higher loads and higher percentage of Exhaust Recirculation (above 30%). Hydrocarbon concentrations and smoke percentage also simultaneously increased indicating poor combustion.
INTRODUCTION
Exhaust emissions from diesel engines are substantial source of air pollution. In recognition of this fact, the regulating authorities of all countries implemented strict regulations which are in effect since 1991. Unfortunately single technology is currently not available to meet these regulations without penalties in engine performance and efficiency. Application of various motor vehicle emission control technologies has established a history of success. This success, however, has largely been offset by the constantly growing numbers of vehicles and miles traveled. Heavy-duty diesel engine manufacturers have developed new technologies in response to increasingly stringent emission standards. The diesel engine has long been a champion of fuel economy.
ETHANOL AS MOTOR FUEL
Historically ethanol and methanol have been used as automotive fuels for long time, both as neat fuels and as blend components chiefly in gasoline engine. Nikolaus Otto, the father of the Otto engine, regarded ethanol as an attractive fuel for combustion engines and in 1908 Henry Ford started the construction and production of an ethanol fuelled engine and claimed that alcohol could be an automotive fuel for the future. Although replacing diesel fuel entirely by alcohols is very difficult, an increased interest has emerged for the use of alcohols, and particularly lower alcohols (methanol and ethanol) with different amounts and different techniques in diesel engines as a dual fuel operation during recent years. Ethanol or ethyl alcohol was used as quality motor fuel in the first automobile, the original Ford Model-T and after that it is only recently that interest was shown in the use of ethanol and methanol as diesel fuels. It is reported that about 80% proof ethanol is optimum as higher proofs do not give as much reductions in oxides of nitrogen emissions [1-2].
DIESEL COMBUSTION WITH ETHANOL
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 inconvenient
effect, injection of ethanol to inlet duct is considered [10].
Ethanol will quickly evaporate (but will not self-ignite),
and will be ignited by burning diesel droplets resulting in
very high combustion rate of both fuels, especially diesel
fuel. With higher combustion rate higher thermal
efficiency, higher power output and lower emission of
HC and smoke are expected. Hence, the combined effect
of ethanol fumigation (without reducing the amount of
diesel being injected) and EGR is expected to reduce
NOx with marginal loss of efficiency when compared to
use of EGR alone.
RESULTS AND DISCUSSIONS
Engine Torque
As expected injecting ethanol will increase the
torque (adds energy) as amount of diesel injected is not
reduced. In the fig.2, the trend of torque at part load of
1.5 kW and maximum load of 2.5kW for 5, 10, 15 and
20% ethanol fumigation are compared with those
corresponding to only hot EGR. Torque values for 5%,
10% and 15% ethanol fumigation are higher as compared
to hot EGR for both part and full load but for 20% values
reduce. At full load torque is almost same for 5, 15 and
20% ethanol fumigation and hot EGR for all percentage
of EGR. 10% fumigation gives the optimum results for all
values of load and EGR percentage.
CONCLUSION
It can be concluded from the results obtained from the experiment that
1. EGR method to abate NOx emission is very effective. The disadvantage is decreased efficiency and increased HC and Smoke with higher percentage of EGR and at higher loads.
2. Ethanol fumigation without altering the diesel injection proves to be a better option in reducing HC, smoke and NOx apart from improving the engine thermal efficiency.
3. Ethanol fumigation above 10% tends to increase HC and smoke emissions when compared to corresponding values for 5 and 10% , however these values are very less as compared to use of EGR without ethanol fumigation.
4. 10% ethanol fumigation with HOT EGR is a better option for higher percentage of EGR to be used with maximum reductions in NOx emissions with marginal loss of efficiency.