A review on natural gas/diesel dual fuel combustion, emissions and performance

With the increasing concern regarding diesel engine emissions, including nitrogen oxides (NOX) and particulate matter (PM), and the rising of energy demand as well, the utilization of alternative fuels in diesel engine has been found to be an attractive solution. Natural gas is a very promising and highly attractive fuel because of its domestic availability, widespread distribution infrastructure, low cost, and clean-burning qualities to be used as a transportation fuel. Natural gas/diesel dual fuel is an operation mode in which natural gas is introduced into the intake air upstream of the manifold and then ignited by the direct injected diesel in the cylinder. The aim of this paper is to identify the potential use of natural gas/diesel dual fuel on diesel engine. In this literature review, the combustion, emission and performance characteristics of natural gas/diesel dual fuel combustion-mode published mainly in scientific journals have been collected and critically analyzed. A wide range of natural gas mass ratio which represents the mass fraction of natural gas in the total fuel and different types of engines were involved. It has been found that dual fuel mode has a lower compression pressure and a longer ignition delay compared with normal diesel mode. The application of dual fuel mode significantly decreases the NOX, carbon dioxide (CO2) and PM emissions. However, the hydrocarbon (HC) and carbon monoxide (CO) emissions may increase by several times or even more than 100 times in comparison to normal diesel combustion. And there appears a trade-off relationship between NOX and HC emissions with dual fuel mode. The engine power is decreased up to 2.1% at dual fuel mode, but the power loss can be reduced or recovered by changing some of the operating parameters. The brake thermal efficiency (BTE) of dual fuel mode is lower at low and intermediate loads, while under high engine load conditions it is similar or a little higher when compared with normal diesel mode, and the maximum increase is about 3%. The COVIMEP seems to be generally higher than normal diesel mode and it decreases with the increasing engine load.