Homogeneous-charge spark-ignited lean-burn natural gas engines have shown considerable promise in reducing exhaust emissions and improving thermal efficiency. A further extension of the lean-limit can be achieved, however, by providing a relatively rich mixture in the vicinity of the spark plug, while maintaining an ultra-lean homogeneous charge in the main chamber area. This further extension of the lean limit using a partial-stratification technique has shown promise in reducing emissions and increasing thermal efficiency. Preliminary data from a novel ultra-lean-burn stratified-charge engine configuration show that this technique can be successfully used to extend the lean limit of operation, and to further improve fuel economy. This paper also reviews earlier experimental data from a series of tests of a single-cylinder research engine operating on natural gas over a range of air-fuel ratios from stoichiometric to the lean-limit of combustion. Combustion chamber design has been found to be very important to ensure complete combustion at very lean operating conditions, and to minimise exhaust emission levels. A comparison of the performance and exhaust emissions using two different engine combustion chamber configurations are reviewed and show that combustion chambers designed to control the turbulence intensity and scale just before ignition can be very effective in improving engine performance and reducing emissions.
A Stratified-Charge Engine Concept for Low Emissions and High Efficiency
1999
Aufsatz (Konferenz)
Englisch
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