Experimental Research On Combustion And Emission Characteristics Of An HCCI Engine Fueled With Coal-derived Naphtha/Isopropanol Blends

The development of the internal combustion engine is facing the challenge of strict laws and regulations.In pursuit of ultra-low emissions and economical fuels,academics have proposed HCCI low-temperature combustion technology,which has higher thermal efficiency,low fuel consumption and high fuel applicability,but also has some shortcomings such as difficult to control the combustion process,large noise and narrow operating range.In this paper,N70IP30（N70IP30 accounts for 70%of the coal naphtha and 30%of the isopropanol volume）,N60IP40,N55IP45,N50IP50 and N45IP55 coal-derived naphtha/isopropanol blends are respectively prepared.On an HCCI engine modified from a 4JK1 diesel engine,the effects of isopropanol blending ratio,intake temperature(T_in),excess air coefficient（λ）and engine speed（n）on the combustion,emissions and machine performance of HCCI engine are explored and discussed,and its operating range is also studied.The results are as follows:（1）With the increase of isopropanol content,the peak of pressure(P_max),heat release rate(HRR_max)and temperature(T_max)decrease during in-cylinder combustion;The phases of combustion startpoint（CA10）and midpoint（CA50）are delayed and the combustion duration（BD）is increased.The cyclic variation coefficient(COV_Pmax)decreases first and then increases,and the COV_Pmax was the lowest when N60IP40 was used,which was 0.62%.CO and HC emissions increase,but NOx emissions reverse.The average indicated pressure（IMEP）rises first and then descends,and the indicated thermal efficiency（η_i）has the same trend.The IMEP andη_i of N60IP40 were the best,which were 0.42MPa and 1.2%respectively.（2）As T_inincreases,P_max,HRR_max and T_max all increase significantly,CA10 and CA50 move forward,and BD decreases.At this moment,the combustion is rapid and the heat release is concentrated.COV_Pmax decreases first and then increases,for N60IP40,COV_Pmax is the smallest at the T_in of 40℃;CO and HC emissions decrease and NOx emissions increase.When the condition is N60IP40,IMEP increases first and then decreases,η_i also shows the same trend.The maximum values of IMEP andη_i are 0.420MPa and 41.15%at 40℃.When the working conditions are N55IP45 and N50IP50,both IMEP andη_i show an increasing trend,and the increasing speed gradually slows down.（3）Asλincreases,P_max,HRR_max and T_max all decrease.CA10 and CA50 are delayed and BD is lengthened;COV_Pmax decreases first and then increases;CO and HC emissions increase and NOx emissions decrease.IMEP andη_i greatly decrease,and the decrease is more obvious when isopropanol content increases.（4）As n rises,P_max,HRR_max and T_max all increase obviously;CA10 and CA50 are advanced and BD is decreased;The COV_Pmax decreases first and then increases;CO and HC emissions decrease,while NOx emissions are the opposite.（5）The operating range:the increase of isopropanol content makes the engine expand towards heavy load,andλof detonation combustion boundary and incomplete combustion boundary decreases gradually;The increase of T_in makes theλof detonation combustion boundary and incomplete combustion boundary increase and move towards the direction of small load.