Diesel Engine Practical

Diesel engine is operated by changing the fuel flow rate to accommodate the variation in the load since such a change alters heat release rate and thermodynamic work. The work done is measured by dynamometer whereas the heat release rate is computed from the cylinder pressure measurement because of the difficulty in its measurement. As being an apparent quantity, the heat release rate is predicted by the double Wiebe function in computer simulation with the constants and correlations proposed in the literature for the Wiebe function parameters. The heat release rate prediction facilitates the simulation of cylinder pressure and work done to negate the experiments. However, the accountability of the computer simulation rest over the accuracy

The potential usage of diesel engines in the heavy duty vehicles generally reduces the fossil fuel consumption because of its higher thermal efficiency. However, the efficiency of the engine changes with the changes in the operating load. Generally, the part load efficiency is lower than the full load efficiency in diesel engines. This efficiency fluctuation is due to the alteration of heat release rate relative to the changes in the load. The heat release rate changes responsible for the efficiency changes are difficult to measure experimentally. However, it is apparently computed from the rate of pressure rise measured during the efficiency determination in the experimental investigation [1-5]. Computer simulation of the heat release rate overcomes the time and cost constraints in the efficiency determination by experiments since the prediction of the changes in the heat release rate responsible for the efficiency changes would reduce the number of experiments required in the performance analysis. Heat release rate and performance simulation can be carried out rapidly by a thermodynamic model. Therefore, a rapid performance simulation method is developed with a thermodynamic model in ‘C’ language for a diesel engine and validated with the experimental data in the

LCF (load correction factor) which is defined as the ratio of mass flow rate input of diesel between a required power output and the optimum power output is entertained to quantify the relationship. The heat release rates are simulated by using the LCF in the single Wiebe function [6-9]. However, the combustion of fuel in compression ignition engine exhibits four phases namely ignition delay, premixed, diffusion and late combustion heat release phases. Two Wiebe function each containing four parameters namely combustion duration, the amount of fuel energy as heat release, efficiency factor and shape factor are used to synthesize the premixed and diffusion combustion phase heat release rates [10]. Some constants and correlations were proposed in the previous research [11] to arrive with these parameters. However, the constants and correlations were based on the assumptions of 99.9% complete combustion during premixed and diffusion combustion phases alone [10, 12] without late combustion. Therefore, the corrections in the parameters that are influenced by the combustion efficiency are proposed in this study along with the inclusion of modelling the late combustion phase. Two different values are considered for premixed and diffusion combustion