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

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. (C) 2013 Elsevier Ltd. All rights reserved.