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Natural gas composition depends on when and where it is recovered. Variations of composition affect the performance of combustion systems and the accuracy of delivered energy in fiscal gas metering. This paper presents a methodology to determine combustion properties of natural gases (higher heating value, Wobbe index and the stoichiometric air-fuel ratio). A pseudo-gas formulation is used to determine a composition of the most influent constituents of the natural gas. The pseudo-composition is then determined by solving a nonlinear system of equations using thermal conductivity at three levels of temperature and the carbon dioxide concentration. The tested natural gases are chosen to represent typical European gases as well as to account for large variations of individual components. The error on the combustion properties is less than 0.5% for the most of the examined gases and below 1% for gases with high carbon dioxide fractions.

Performance of a compression ignition engine fuelled with animal fat and its emulsions as fuel is evaluated. A single cylinder air-cooled, direct injection diesel engine developing a power output of 2.8 kW at 1500 rev/min is used. Base data is generated with standard diesel fuel. Subsequently, animal fat is modified into its emulsions using water and methanol. Comparison is undertaken with diesel, neat animal fat and its emulsion as fuels. Results show improved performance with animal fat emulsions as compared to neat fat. Peak pressure and rate of pressure rise are increased with animal fat emulsions due to improved combustion rate. Heat release pattern shows higher premixed combustion rate with the emulsions. Higher ignition delay and lower combustion duration are found with animal fat emulsions than neat fat. Drastic reduction in black carbon smoke and NO are found with the emulsions as compared to neat animal fat and neat diesel.

The crude oil depletion, as well as aspects related to environmental pollution and global warming has caused researchers to seek alternative fuels. Biogas is one of the most attractive available fuels. It is of great interest both economically and ecologically. However, it faces problems that may compromise its industrial use. The dual-fuel engines have been investigated as a technique for the recovery of these gases and finding solutions to these problems. In the present work, performance and emissions of a direct injection diesel engine were first evaluated in conventional mode and dual fuel mode. The effect of biogas composition, based on methane content, is then examined. Also, dual fuel operation with regard to knock is investigated. The results show that, up to 95% of engine full load, the brake thermal efficiency (BTE) is lower in dual fuel mode. In terms of the specific consumption, although at high load the gap is much less, it is more significant in case of dual fuel mode.