Among the different efforts towards the reduction in pollutant emissions from direct injection (DI) diesel engines, the use of gaseous fuels as a partial supplement for diesel fuel has been proposed by many researchers. These engines are known as dual fuel engines. An experimental investigation was performed to investigate the influence of dual-fuel combustion on the performance and exhaust emissions of a DI diesel engine fueled with natural gas (NG) and biogas. In this work, the combustion pressure and the rate of heat release were evaluated experimentally in order to analyze the combustion characteristics and their effects on exhaust emissions including particulate matter (PM) for single-fuel (diesel) and dual fuel combustion modes. The use of NG as an alternative fuel is a promising solution.Biogas, on the other hand, is a renewable alternative fuel that has tremendous potential to be used in diesel engines especially in developing nations. Comparative results are presented revealing the effect of dual fuel combustion on engine performance and exhaust gaseous and PM emissions for the engine operating conditions considered in this study.

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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 the combustion parameter, ψ to describe the completeness of combustion. This parameter is based on the Rassweiler-Withrow method of calculating the 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 analysed with a combustion analysis package. A computer simulation was then used to model the data on a cycle-by-cycle basis, both with and without the completeness of combustion parameter. The paper discusses the conditions under which it is suitable to model mean engine cycles, compared with the need to model cycle-by-cycle variability, and comments on the situations in which each type of modelling would be most appropriate. The engine simulation model is also used to investigate cycle-by-cycle variability of NO emissions that have recently been obtained experimentally. The successful aspects of this investigation are that the cycle-by-cycle variability in the completeness of combustion can be determined by use of the parameter ψ, that the inclusion of the completeness of combustion parameter improves the simulation's ability to model the experimental data both in a statistical sense (the coefficient of variation of the indicated mean effective pressure) and on a cycle-by-cycle basis and that cycle-by-cycle NO modelling results are found to compare well with experiment.

This paper investigates a number of new approaches to mass fraction burned analysis for application to spark ignition engine combustion processes. The rationale for these new approaches is to retain the simplicity and computational efficiency of the technique of Rassweiler and Withrow, but to overcome some of the limitations inherent in the standard methods. The approaches investigated include the use of a two-zone model to determine information about the burned and unburned gas temperatures and the modification of the standard Rassweiler and Withrow expression to incorporate polytropic indices for compression and expansion.The investigation makes use of an engine simulation model, which was used to generate the pressure data. This technique provided a`known' burn rate against which to evaluate the methods investigated. Some experimental data taken from a Rover K4 optical access engine is also presented.The successful aspects of this investigation are the use of the Rassweiler and Withrow equation with different compression and expansion indices, and the application of this analysis to investigate crevice gas burn-up. What was found to be not successful was the use of a two-zone model for calculating gas temperatures. The results indicate that the model is, in general, not reliable for computing temperatures and this is due to the temperature gradient in the burnt zone and the disproportionately high rate of heat transfer from the mixture that burns first during combustion. The mass fraction burned calculations using this model were also found to be not as accurate as those based on simpler models. NOTATION m mass n polytropic index n c polytropic index for compression n e polytropic index for expansion n9 polytropic exponent for the unburned portion of the charge (determined from the compression P± V diagram) n0polytropic exponent for the burned portion of the charge (determined from the expansion P± V diagram) P pressure P t observed pressure during combustion at time t P tf observed pressure at end of combustion P ti observed pressure at ignition R gas constant T temperature V volume V t total volume of combustion chamber during combustion at time t V tf total volume of combustion chamber at end of combustion V ti total volume of combustion chamber at ignition V 0 t

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Particulate matter (PM) emitted from a dual fuel engine is characterized using thermogravimetry, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Thermogravimetric analysis (TGA) provides the mass fractions of elemental carbon and volatile materials in PM; XPS provides the possible chemical compositions in the topmost layer of PM surface and Raman analysis provides the possible structure of the carbon presented in PM. Dual fuel engine uses both liquid (diesel) and gaseous fuels simultaneously to produce mechanical power and can be switched to only diesel fueling under load. The dual fuel engine is operated with natural gas and simulated biogases (laboratory prepared) and results are compared between the dual fueling and diesel fueling under the same engine operating conditions. Significantly higher volatile fractions in PM are obtained for dual fueling compared to diesel fueling complementing the gravimetric results. The maximum contribution of the graphitic carbon or aliphatic carbon such as hydrocarbons and paraffins (C C or C C) are found in the topmost atomic layers of both the diesel and dual fuel PM samples. The other chemical states are found to be the carbon-oxygen functional groups indicating significant oxidation behavior in the PM surface. Lesser aromatic content is noticed in the case of dual fuel PM than diesel PM. The carbon in dual fuel PM is found to be more amorphous compared to diesel PM. These characterizations provide us new information how the PM from a diesel engine can be different from that from a dual fuel engine.