ADVANCED COMBUSTION SYSTEMS AND ALTERNATIVE POWERPLANTS

Historical Overview

For many decades the researchers have pursued development of direct injection stratified charge SI engines to have overall very lean engine operation for higher fuel efficiency. Charge stratification is a means of ensuring repeatable ignition without misfire and stable combustion while using overall very lean fuel-air ratios that is otherwise not possible with homogeneous mixtures. In the stratified charge engines, the mixture composition is varied within the combustion chamber such that stoichiometric or slightly richer mixture exits near spark plug to provide good ignition characteristics and the mixture gets progressively leaner away from the spark plug. Overall air-fuel ratio in the cylinder is significantly leaner than the stoichiometric.
A typical configuration of DISC engine is shown on Fig 7.1. Liquid fuel is injected in the cylinder. The fuel spray is directed by air motion or by the geometry of piston crown or by combination of the both towards spark plug. By the time fuel spray reaches the spark plug electrodes some fuel gets vaporized and forms combustible mixture with air.  The vaporized fuel in spray is then ignited by spark, combustion begins and the flame spreads in the combustion chamber.