Throttleless Premixed-Charge Engines: Concept and Experiment

Abstract

A method of controlling the brake mean effective pressure (b.m.e.p.) of a premixed-charge engine is proposed which does not require the use of a throttle and does not exhibit significant throttling losses. In this method, a combination of adjustment of the mixture equivalence ratio and preheating of the mixture is used to control the b.m.e.p. The preheating serves two purposes: it reduces the density of the mixture and it broadens the lean misfire limit. Experiments on the performance of engines controlled with this strategy are compared with conventional throttled engines. As much as 16 per cent improvement in thermal efficiency was observed at the same b.m.e.p. The untreated NO_x emissions are found to be much lower in the throttleless engine at the same b.m.e.p. while carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions are comparable to but somewhat higher than throttled engines. Practical implementation of the concept is discussed.