Combustion Performance Analysis For A Miniature Reciprocating Internal Combustion Engine With Glow-ignition

Owing to super energy and power density,miniature reciprocating internal combustion engine is widely used in propelling unmanned air vehicle and other portable devices.Limited by the micro size,combustion problems like low combustion efficiency and poor combustion stability become more prominent for miniature internal combustion engine.For this purpose,a miniature internal combustion engine with displacement of 0.99 cc is investigated.The influence of thermal condition and glow intensity on combustion characteristics for the prototype engine is evaluated,and the mechanism of abnormal combustion phenomenon is also investigated.The main contents are as follows:Firstly,in order to evaluate the basic combustion characteristics of miniature internal combustion engine,the paper compared the combustion characteristics of the prototype engine to a most representative conventional two-stroke internal combustion engine.Meanwhile,comparing its combustion characteristics to three miniature engines with the same size level to know its combustion problems with size scaling down.Results show that miniature internal combustion engine has late and disperse CA05,high cyclic variation and poor combustion tability.With the size scaling down,combustion characteristics deteriorate gradually.Hence,taking effective measures to advance CA05,which then improve the combustion characteristics of miniature internal combustion engine is the key to scale its structure down further into meso-scale.The influence of thermal condition on combustion characteristics of miniature internal combustion engine is evaluated.Results reveal that with cylinder block temperature rising,CA05 advance and become more concentrated,and the cyclic variation reduce remarkably.Highing cylinder block temperature can improve combustion stability and combustion characteristics for miniature internal combustion engien.Analysis for inflence of thermal condition on combustion characteristics of macro engien shows that,the effect of thermal condition on internal combustion engien is greater with the size scaling down.The decreasing range of pmi caused by increasing cylinder block temperature for miniature internal combustion engine is more than 50 times as macro engien,which indicates that thermal condition is a significant facter to ensure normal operation when ministure intenal combustion engine scaling down.Combustion characteristics for normal combustion condition and limiting misfiring condition are respectively diagnosed under different current intensity.Finding that with the increasing of the current intensity,under normal combustion condition,cyclic variation and misfiring rate for miniature internal combustion engine increase.As for limiting misfiring condition,enhancing the glow intensity remarkably contributes to solve the problem of high misfiring rate which is caused by failed ignition and improve combustion stabiity.Switching on current to the platinum wire has negative impact on combustion for miniature internal combustion engine under normal combustion condition,while for limiting misfiring condition,combustion stability can indeed be improved.Therefore,electrical heating glow-ignition combustion can be considered as one of underlying approaches to extend the limiting combustion regime especially for prospective meso-scale IC engines.Aiming at the prominent abnormal combustion phenomenon for miniature intenal combustion engien,the way of analyzing individual cycle is proposed,wich analyzes the combustion influence for characteristic cycles and its adjacent cycles to investigate the generation macanisum of abnormal combustion.Results indicate that under glow strengthening condtion,more than 70% of AC cylces are occurred in F+1 cycles,which indicates that excessively advancing CA05 is the main reason to cause abnormal combustion.When no current switching on to the platinum wire,under normal combustion condition,excessively advancing CA05 has light negative effect on F+1 cycles,but no AC cycles are occuring.When combustion methanol bleng fuel with 30% of nitromethane and methanol bleng fuel with 10% of hydrogen peroxide,about 50% of AC cycles occuring in F+1 cycles reveals that excessively advancing CA05 is one of the significance reason to cause abnormal combustion.When combustion methanol bleng fuel,much more than 83.33% of AC cycles occurring in F+1 cycles indicate that excessively advancing CA05 is the main reason to cause abnormal combustion.