Experimental Study On Combustion And Emission Characteristics Of Diesel Fuel Blending With Fatty Acid Methyl Ester (FAME)

Confronted with increasingly stringent emission laws,people no longer merely take the dynamic and economic performances of the alternate fuel into consideration,but concern more about the performance of emissions.Recently,fatty acid methyl esters have been proved to be an appropriate alternative for diesel.And they can be directly burned in the conventional diesel engine via mixing with diesel properly,which will alleviate the shortage of energy.Firstly,an experimental study of burning four mixtures containing 20%different short chain fatty acid methyl ester(methyl hexanoate,methyl octanoate,methyl decanoate and methyl hexenoate)was conducted on a modified diesel engine,which was to investigate the effect of molecular structure of fatty acid methyl ester on the combustion and emission characteristics of the mixture.The experiment results show that low combustion temperature under low engine load resulted in poorer CO emissions,and adding methyl hexanoate into diesel fuel will obviously deteriorate CO emission.Comparing with diesel,PM emissions decrease under all load when the diesel is mixed with methyl hexanoate,but they are still higher than those of the other three mixtures.under the low load,insufficient combustion of fuel results in lower indicated thermal efficiency for all mixtures,and adding methyl hexanoate into diesel produces the lowest indicated thermal efficiency.Secondly,the experiment was conducted by adjusting different combustion parameters and using different injection strategy,which was to optimize the combustion process and reduce emission.Results show that as direct injection timing delays,CO and HC emissions increase progressively while NOx emission decreased,and PM emissions of diesel also increase.Besides,indicated thermal efficiency increases initially and then decreases.As EGR rate increases,CO emissions increase while NOx emissions decrease,and HC emissions almost maintain steady.PM emissions of diesel also increase.And the indicated thermal efficiency experiences a dramatic decrease under high EGR ratio.When the pilot injection ratio is 20%,as pilot injection timing delays,CO and HC emissions decreased,NOx emissions decreased slightly and particulate emissions gradually reduced,the indicated thermal efficiency is gradually increased.Finally,the experiment was conducted under low temperature combustion mode to further investigate the combustion and emission characteristics of the mixtures.And the EGR rate was kept at 40%.Results show that when the pilot injection ratio is 20%,pre-ignition phenomenon only exists as the pilot injection timing is postponed to-40°CA ATDC.In comparison,when pilot injection ratio is 40%,pre-ignition phenomenon already exists as the pilot injection timing is-60°CA ATDC.Moreover,higher pilot injection ratio will worse CO and HC emissions,improve NOx emissions,and reduce the indicated thermal efficiency.Lower pilot injection ratio will lead to higher nuclear mode particle emissions while higher pilot injection ratio will lead to higher accumulation mode particle emissions.