A Theoretical Study of the Influence of Operating and Design Variables on the Duration of Combustion in the Spark Ignition Engine

摘要

A previous report stressed the crucial importance of the duration of the combustion period in any move towards the higher compression ratios and leaner mixtures that offer a route to increased thermal efficiency of spark ignition engines. A relationship was suggested between the time of combustion and the most important general governing factors. In the present report this treatment is further developed to arrive at a simple working equation which relates the degrees of crank angle for complete combustion (C) to specific engine operating and design variables, viz, engine speed (N), laminar burning velocity of combustible mixture (S), distance between spark plugs and furthermost wall (D), radius of flame kernel produced by spark (r), and a fluid-dynamic characteristic of the engine (K). The assumptions underlying the equation are displayed and discussed. Simple comparisons with known data suggest that the equation is broadly correct in its prediction of many effects, but more careful and extended study is required. In particular the physical significance of the important factor K which dominates the equation requires further exploration.