Study On Combustion And Emission Characteristics Of An HCCI Engine Fueled With N-Butanol/Gasoline Blends

Considering continuously stringent emission regulations,as well as increasing shortage of petroleum resources,the development of new highly efficient and environment friendly combustion methods has become increasingly important.Homogeneous Charge Compression Ignition（HCCI）,as a new combustion method,has become one of the hot topics in the field of internal combustion engines due to high thermal efficiency,ultra-low NOx and soot emissions,and strong fuel adaptability.However,HCCI faces many challenges,such as uncontrollable combustion phasing and narrow operating range and so on,hindering the commercial application of HCCI combustion technology.In this paper,different mixing ratio n-butanol/gasoline blends（the volume ratio of gasoline in the blended fuel is defined as the fuel mixing ratio）are used as fuel for the HCCI engine.The HCCI combustion is conducted on a modified two-cylinder diesel engine to investigate the effects of fuel mixing ratio,intake temperature(T_in),excessive air ratio（λ）and engine speed（n）on the combustion and emission characteristics as well as the performance of an HCCI engine.The experimental results show that with the increase of gasoline mixing ratio,for the four test fuels,the peaks of in-cylinder pressure(P_max),temperature(T_max)and heat release rate(HRR_max)initially increase and then reduce,The operating range of HCCI engine is extended to both high-load and low-load areas.When the volume fraction of gasoline is 10%,HC and CO emissions are the lowest,the indicated mean effective pressure（IMEP）and thermal efficiency（η_i）all reach the maximum,the engine comprehensive performance is the best.In addition,the T_inhas a significantly effect on the n-butanol/gasoline HCCI engine.As the T_inincreases,P_maxand HRR_maxof four test fuels increase gradually,the combustion phase advances and the HC and CO emissions reduce,while NOx emissions slightly increase.The best T_inis 130℃,where the IMEP andη_iachieve their maximum.Furthermore,With the increase ofλ,the P_max,T_maxand HRR_maxof four test fuels show monotonously reducing trend.At the same time,the change of CA10 is not obvious,the BD extends,and the HC and CO emissions increase.The IMEP monotonously decreases,however,theη_ifirstly slightly increases and then reduces,the bestλis 2.5,where theη_iachieve maximum.Finally,the n has a little effect on the in-cylinder pressure and temperature,with the n increases,CA10 and CA50 are advances,BD slightly decreases,COV_Pmaxfirstly reduces and then increases.When n is 1200r/min,the COV_Pmaxis minimum,too high or low n is not conducive to the stable operation of HCCI engine.