The Study Of The Combustion Process And Knocking Mechanism In Spark-ignition Methanol Engine

From the engineering application perspective, methanol is an ideal alternative,renewable, environmentally and economically attractive fuel. In the1990s, thesouthwest research institute proposed a high compression ratio spark-ignitionmethanol engine program which provides a new idea for the development of highpower and high efficiency methanol engine. The study of the combustion andknocking suppressing mechanism for the spark-ignition methanol engine is the corescientific engineering technology issue, and its findings can provide adequatetheoretical guidance to the development of the spark-ignition methanol engine,promoting the rapid maturity of the technology so as to meet the market demand.Therefore, in this paper, the ignition process, combustion and emissions, andknocking suppressing methods were studied in a spark-ignition methanol engine.Firstly, in this paper, the ignition in a spark-ignition methanol engine was studiedby using LES (large eddy simulation) with detailed chemical kinetics. The studyincluding: the effects of flame kernel size, flame kernel surface temperature for theMIE (minimum ignition energy) and IDP (ignition delay period) in a spark-ignitionmethanol engine. The simulated results showed that using smaller flame kernel couldincrease the demand for MIT (minimum ignition temperature), and using smallerflame kernel could decrease the demand for MIE. The demands of the MIT and MIEhad complementary correlation, that was, as the MIT decreased, the MIE increased.Secondly, in this paper, combustion emissions under various engine operatingconditions were simulated, and the effects of sparking timing, compression ratio,engine speed, mixture concentration and combustion chamber shape for emissions ina spark-ignition methanol engine were studied based on the LES with detailedchemical kinetics. The results showed that there exist two effects for CH2O, whichwere generation and consumption. The produced CH2O in the combustion process ofmethanol was consumed quickly, so the mass fraction of residual formaldehyde wasvery low after complete combustion and could be ignored.Thirdly, in this paper, knock in a spark-ignition methanol engine was studied byusing multi-dimensional simulation. Knocking combustion under various engine operating conditions were simulated, and the effects of spark timing, EGR (exhaustgas recirculation) techniques, mixture concentration and combustion chamber shapefor suppressing knock in a spark-ignition methanol engine were studied based on themulti-dimensional simulation analysis. Through the established model, from theperspective of chemical reaction kinetics to explore the knocking combustion process,the results showed that the use of a high EGR rate and early spark timing had a betterthermal efficiency on the knock suppression as compared to the use of a low EGR rateand late spark timing. OH radicals could be a good temperature indicator and played apredominant role during the knocking combustion. The concentration of HCO radicalswas almost negligible during knocking combustion. There existed two effects forCH2O, OH and H2O2, which were generation and consumption.Finally, in this paper, for the needs to study knocking combustion phenomena,this paper developed an ORCEM (optical rapid compression and expansion machine)based on the principle of hydraulic. The compression ratio of ORCEM is adjustable. Itis simple, compact, and it also provides the possibility for the in-cylinder knockingcombustion phenomena to be visualized experimentally. In this paper, the movementlaw and knocking combustion phenomena were studied by using bothone-dimensional and three-dimensional simulations, and the simulated results showedthat the developed ORCEM could simulate the compression and expansion process,and could be used to study the knocking combustion phenomena.