Charge stratification for an internal combustion engine
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
The effect of charge stratification on the lean mixture combustion in a Ricardo E6 single cylinder, variable compression, spark ignition engine has been investigated. The charge stratification process involved injecting small amounts of pure methane gas into the engine cylinder through a modified spark plug just prior to ignition, at a relatively low pressure. Methane injection timing and methane injection duration (or injection rate) were controlled electronically and varied over a range of values. The charge stratification experiment was performed with two different types of inlet mixture. They were :- (1). gasoline fuel injected into the inlet manifold (2). methane gas carburetted through the inlet manifold To examine the effects of charge stratification, a few optimisation studies were undertaken prior to the main combustion experiments. A combustion chamber simulation was performed to visualise the effects of the velocity field on the injected methane gas. For this a constant volume bomb was built with the same bore as that of the Ricardo engine cylinder. A typical set of velocity fields around the spark plug gap location were established using hot wire anemometry, and relevant positions of the injected methane gas at different times from the injection point in the simulated velocity field were captured through Schlieren photography. The present work has led to the following conclusions:- (1). lean limit of the inducted fuel mixture is extended through the charge stratification process (2). effectiveness of charge stratification is well pronounced at lean air - fuel ratios (3). HC emission is higher with stratified charge combustion compared with base line operation (4). CO emission with stratified charge combustion is almost the same as or little lower than with base line operation, at leaner air - fuel ratios (5). the initially small and compact shape of the injected methane gas appearing in the Schlieren photographs could have a positive influence on the flame initiation phase.