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With the increasing concern regarding diesel engine emissions, including nitrogen oxides (NO X ) 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 NO X , carbon dioxide (CO 2 ) 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 NO X 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 COV IMEP seems to be generally higher than normal diesel mode and it decreases with the increasing engine load. [ABSTRACT FROM AUTHOR]

In this study, port premixed methanol compression ignition combustion was performed on a heavy-duty diesel engine. The effects of methanol to diesel ratio (R MD ) and DIT (diesel injection timing) on combustion, performance and emissions were comprehensively investigated. The experimental results demonstrated that R MD and DIT played important roles in combustion and emission control. With the increasing R MD , the ignition delay was prolonged and the combustion duration was shortened. And as DIT retarded, the ignition delay was also prolonged and the combustion duration basically remained unchanged at the beginning, and then followed by a slight decrease. The maximum in-cylinder mean temperature decreased with the retarding DIT and it was largely affected by the combine of R MD and DIT. The brake thermal efficiency remained stable at low R MD , but showed a slight decrease at high R MD. NO X and soot emissions and the RI (ringing intensity) were all decreased as RMD increase, while HC and CO emissions increased significantly. With the retarding DIT, HC emission firstly increased and then decreased, while CO emission always increased. It was more important that the trade-off relationship between NO X and soot was significantly improved with the increasing R MD and almost disappeared at R MD 1.54. [ABSTRACT FROM AUTHOR]

The combustion and emission characteristics of a dual fuel diesel engine with high premixed ratio of methanol (PR m ) were investigated. Experiments were performed on a 6-cylinder turbocharged, inter-cooling diesel engine. Methanol was injected through the intake port and ignited by direct injected diesel in the cylinder, the maximum PR m was over 70%. The experimental results showed that with high PR m , the maximum in-cylinder pressure increased from medium to high engine load but varied little or even decreased at low engine speed and load. High PR m prolonged the ignition delay but shortened the combustion duration and decreased the in-cylinder gas temperature at ignition timing. Hydrocarbons (HC), carbon monoxide (CO), formaldehyde emissions and the proportion of nitrogen dioxide (NO 2 ) in nitrogen oxides (NO X ) increased significantly with the increase of PR m while NO X and dry soot emissions were significantly reduced, which meant the trade-off relationship between NO X and soot emissions disappeared. The increased HC, CO and formaldehyde emissions could be effectively reduced by diesel oxidation catalyst (DOC) when the exhaust gas temperature reached the light off temperature of the DOC. After DOC, the NO 2 proportion in NO X was greatly reduced to less than that of baseline engine at methanol premixed mode but increased slightly at pure diesel mode. The maximum PR m was confined by in-cylinder pressure at high engine speed and load. But at low engine speed and load, it was confined by the high emissions of HC, CO and formaldehyde even after DOC. [ABSTRACT FROM AUTHOR]