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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.

To investigate the combustion stability in a natural gas engine at idle, the burn parameters are determined on a cycle-by-cycle basis through the analysis of the engine pressure data. Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The parameters lowest normalized value (LNV) introduced by Hoard and Rehagen and coefficient of variation (COV) are used to investigate the combustion stability at idle. Measurements of combustion pressure are used to determine values for these parameters in a Ricardo research engine. The fuel used natural gas, and compression ratios between 6 and 14 are explored. The objective of this work is to identify whether these variables are a significant source of cycle-by-cycle combustion variability in a natural gas engine at idle.

The performance and combustion characteristics of a miniature two-stroke, glow ignition engine are investigated. The objective of the work is to determine the effects of three independent variables, namely: the proportion of nitromethane in the fuel, glow plug rating (‘cold’, ‘medium’ and ‘hot’), and air/fuel ratio, in order to improve understanding of the engine performance and combustion processes. Analysis of the data has shown that all of the parameters varied have an important effect on the performance and combustion characteristics of the engine.

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.

This paper investigates a technique of calculating the completeness of combustion on a cycle-by-cycle basis. The technique introduces the normalized pressure rise due to combustion parameter (Ψ) to describe the completeness of combustion. This parameter is based on the Rassweiler and Withrow method of calculating mass fraction burned and is derived from the pressure-crank angle record of the engine. Experimental data were obtained from a Rover K4 optical access engine and analyzed with a combustion analysis package. A computer simulation was then used to model the data on a cyclic basis, both with and without the completeness of combustion parameter. The inclusion of completeness of combustion improved the simulation's ability to model the experimental data both in a statistical sense (COV of IMEP) and on a cycle-by-cycle basis.

A medium size diesel engine converted to natural gas operation on the Otto principle has been studied under stoichiometric and lean burn operation in order to evaluate the potential to reduce the NOX exhaust gas emissions below the stringent limit prescribed by the Swiss Federal Clean Air Act - 250 mg/mN3, 5%O2 (at normal (N) conditions, 5 % residual oxygen and dry). While both operational modes fulfill the prescribed NOX limit, lean burn operation, combined with turbocharging, provides a higher brake power and a better fuel conversion efficiency.

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.