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Research on the combustion and performance of dual fuel stationary engines using natural gas and methane is found to be adequate in published literature. The emissions aspects, however, are less well investigated. Inadequacy is also noted in the case of published research works on biogas in dual fuel engines in respect of regulated emissions. One important pollutant which has not received much attention among researchers is the particulate matter (PM) for such applications. Though it is often claimed that PM emissions from gas-diesel dual fuel engines are much reduced, few works have been published to support this claim. The present study is intended to help fill the gap and all the regulated emissions (CO, CO2, NOx, UHC) including PM are measured for a Lister Petter direct injection stationary diesel engine modified for dual fuel applications. Two alternative gaseous fuels used in this study are natural gas and biogas.

A light scattering photometer has been used to measure the diesel particulate emission from a vehicle to assess the capability of this instrument by comparing with the results from the traditional filter collection method and also with an opacimeter. Tests were conducted on a diesel vehicle mounted on a chassis dynamometer with its exhaust directed to a double dilution tunnel. Different types of test were carried out, including steady speed tests at different engine loads and transient tests. It was found that the correlation between the average particulate mass concentrations determined from the photometer and the filters changed with engine operating conditions. Comparison between the real-time outputs from the photometer and the opacimeter showed an excellent agreement in their particulate emission patterns measured during the transient tests. In conclusion, the photometer demonstrates a good potential in its application to diesel particulate measurements.

Steady state experiments on a single cylinder spark ignition engine were performed to investigate the effects of compression ratio on nitric oxide and hydrocarbon emissions using natural gas as the fuel. Compression ratios between 8 and 15 were investigated. Constant throttle tests were performed at different equivalence ratios, throttle openings and spark timing settings covering a wide range of these parameters. In general, nitric oxide and hydrocarbon emissions were found to increase with compression ratio at fixed spark timing. With optimised (MBT) spark timing, however, reductions of emissions could be achieved at high compression ratio. This indicates that a fully optimised natural gas fuelled engine may be able to achieve high efficiency and low emissions.