A Partially Stratified-Charge Approach for Reduced Emissions From Gas Engines

Previous work has shown that a novel partially stratified-charge approach can be effective in extending the lean limit of combustion and reducing the exhaust emissions from natural gas-fueled engines. The new technique provides a relatively rich mixture in the vicinity of the spark plug, while maintaining an ultra-lean homogeneous charge in the main chamber area. In order to provide the near-stoichiometric mixture near the spark gap, a small quantity of "pilot" fuel is injected through the spark plug just prior to ignition. It has been found that for most operating conditions the required pilot fuel quantity is less than 5% of the total fuel charge. This paper also reports the results of some recent one-dimensional computer modelling in which the partially stratified-charge technique has been investigated over a range of air-fuel ratios. The results show that the improved combustion performance, particularly during ultra-lean operation, provides reduced levels of both fuel consumption and exhaust emissions.