Effect of adding oxygen to the intake air on a dual-fuel engine performance, emissions, and knock tendency

Abstract

Dual-fuel gas-diesel engines present an environmentally attractive substitute for conventional diesel engines that operate with a finite resource petroleum fuel and emit large amount of harmful emissions. However, this engine configuration, in which the gaseous fuel is used as a primary fuel while the diesel fuel is used as an ignition source, suffers from lower thermal efficiency, slower burning rate, and higher CO (carbon monoxide) and HC (unburned hydrocarbon) emissions; particularly at part loads. Prolonged ignition delay and increased tendency to knock are other negative aspects of these engines.The addition of oxygen to the intake air, commonly known as oxygen-enrichment, is expected to partially resolve these problems. In the present experimental study, a single-cylinder DI (direct injection) diesel engine has been properly modified to run on dual-fuel mode with natural gas as a main fuel and diesel fuel as a pilot; with the ability to enrich the intake air with variable amounts of oxygen. Comparative results are given for both plain dual-fuel (without oxygen-enrichment), and dual-fuel with different percentages of oxygen-enrichment of the intake air, at different load conditions; revealing the effect of adding oxygen to the intake air on engine performance, emissions, and knock tendency.