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Determination of knock start for any engine tuning remains a difficult work for many engine manufacturers. This study investigates different combinations of existing knock indices in order to produce an upgraded indicator easier to calibrate. Experiments were conducted on a single-cylinder gas engine bounded to combined heat and power (CHP). Effects of spark advance, volumetric efficiency and equivalent ratio are studied under constant speed operation. The ratio IMPO / MAPO (with IMPO defined as the Integral of Modulus of Pressure Oscillation and MAPO as the Maximum Amplitude of Pressure Oscillation) is proposed as a suitable indicator. In any engine setting, it remains constant under non knocking conditions. When knock occurs, a model deduced from dimensionless analysis allows to determine the oversteps of Knock Limited Spark Timing from IMPO / MAPO measurements with an accuracy lower than 1 CA.

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.