| Internal combustion engine as a huge energy consumption and emission groups have always been the concentration of energy conservation and emission reduction.Homogeneous Charge Compression Ignition（HCCI）is widely considered to be an excellent strategy to meet the requirements of environmentally friendly power equipment because of its high thermal efficiency,low pollutant emissions,and strong fuel applicability.Nevertheless,due to the difficulty of controlling the combustion process and the narrow operating range,the commercialization process is slow.This paper selected different mixing ratios of n-butanol/coal-derived naphtha blended fuel for test（the proportion of n-butanol volume in the blendeded fuel is defined as the mixing ratio）,based on a modified CT2100Q diesel engine,the HCCI combustion and emission characteristics of four fuels with different mixing ratios at different intake temperature(Tin),excess air ratio（λ）and engine speed（n）were studied.The engine performance and operating range under different boundary conditions were also analyzed here.The test results show that as the mixing ratio of n-butanol increases,the peaks of in-cylinder pressure(Pmax),heat release rate(HRRmax)and temperature(Tmax)of the four blended fuels gradually decrease,and the corresponding phase shift backward;The start combustion timing（CA10）and main combustion timing（CA50）delay,the combustion duration（BD）extends;Coefficient of cyclic variation of the peaks of in-cylinder pressure(COVPmax)have a minimum value at a certain mixing ratio;NOx emission decreases,while CO and HC emissions show a same trend with COVPmax whenλare 3.0 and 3.5,and keep increasing whenλis 4.0;The indicated mean effective pressure（IMEP）and indicated thermal efficiency（ηi）decrease with the increase of the mixing ratio,but the corresponding load range becomes wider.When the mixing ratio is relatively low,Pmax and Tmax decrease first and then increase with the increase of Tin,while the mixing ratio is relatively high,Pmax and Tmax increase all the time,but the phase advance trend corresponding to the peak value is the same;With theincrease of the mixing ratio,the combustion phase bring forword and BD shortens;The peak of in-cylinder average pressure(`Pmax)gradually increases,and COVPmax decreases;CO and HC emissions reduce,and NOx emission increase;IMEP andηi both increase first and then decrease,The increase of Tin broadens the load range,and the overall operating range expands to low-load conditions.With the increase ofλ,Pmax,Tmax and HRRmax have the same trend of reduce,and the corresponding phase all shift back,CA10 and CA50 delay,and BD extends.reduces`Pmaxreduces,and the deterioration of combustion stability leads to an increase in COVPmax;CO and HC emissions increase,while NOx emission decrease.Engine speed n also has a great effect on HCCI.As n increases,Pmax,Tmax and HRRmax all increase gradually,and the corresponding phase shifts slightly forward;CA10 and CA50advance,and BD shortens;The least COVPmax appear at the intermediate speed because of the best combustion stability;The NOx emission increase gradually,while the CO and HC emissions present an opposite trend. |
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