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Variable composition of natural gas depending on the gas source causes variable ignition and combustion properties when used as fuel in internal combustion engines. Ignition and combustion problems lead to reduced efficiency, increased levels of emissions, as well as increased mechanical and thermal loads on engine components. The main objective of this study is to investigate the influence of natural gas composition on ignition properties in a direct injection hot surface assisted compression ignition engine. Previous investigations have shown that ignition of methane require hot surface temperature in the range of 1200-1400 K in order to obtain an ignition delay within 2 milliseconds. Pure methane and several natural gas mixtures have been tested under various conditions in a constant volume combustion bomb and in a test engine. Ignition delay and cycle to cycle variations are used to compare the combustion qualities of the different gas.

The objective of this paper is to introduce a new method for full-field measurement of local average gas-phase fuel concentration in a transient axisymmetrical gas-jet or evaporating spray. Since the combustion process in a diesel engine is a diffusion flame, the local fuel concentration as a function of time is one of the factors that governs engine efficiency and emissions. The method is utilizing the classic Schlieren technique. A CCD camera and frame-grabber combination is used to record the data. Based on these data and the assumption that the flow-field is axisymmetrical, the local index of light refraction is calculated, and from this an estimate of the local gas-phase fuel concentration is made. Since the flow-field is turbulent, data from a large number of separate injections are used. Therefore the results should represent the development of the average flow-field. Since it is a full-field method, the results can be checked for overall conservation of mass.

Burning natural gas in a direct injection diesel engine, requires a special arrangement to secure ignition. In this study a hot surface assisted ignition concept is investigated in a constant volume combustion bomb and a test engine with the objective to develop a better understanding of the mechanisms involved. The experiments show that surface temperature above 1200 K is required to achieve acceptable ignition, strongly dependant on natural gas composition and system parameters such as injection and hot surface geometry. A mathematical model of the concept is also being developed. Numerical simulations combined with experiments allow us to look closer into the processes, and to expand the test matrix even outside the physical limits of the test engine. This paper will give an outline of the investigation including some results from experiments and numerical simulations.