Heat transfer in reciprocating combustion engine is an intricate phenomenon involving rapid cyclic variation of cylinder pressure temperature density and area of contacting surfaces. Rate of heat transfer in internal combustion engine is further complicated greatly due to the gas turbulence and flame radiation effects, the magnitudes of which depend on the engine type and operating conditions. It is necessary to calculate the heat flow, the temperature distribution and the temperature stresses. Hence, an accurate model for estimation of heat transfer in various phases of the cycle is an important factor which influences the accuracy of all parameter in the cycle analysis.
Nearly more than twenty correlations have been proposed to find the heat transfer coefficient in the combustion chamber wall among which some of theoretical concepts. The large disagreement among the various proposed formulae for reciprocating engine heat transfer made it hard to choose any adequate e formula for universal application to various combustion engines
This paper proposes a modified heat transfer correlation based on experiments conducted in motored diesel engine with natural aspiration of hot air at around 150°C-300°C. The author considered the Intake jet velocity in place of mean piston speed in Reynold parameter in proposed heat transfer coefficient equation. The Intake jet velocity is better representative of gas velocity than the mean piston speed since it takes into account the diameter of inlet port of an engine and diameter of piston. Further, the proposed heat transfer correlation for Compression Ignition engine is validated by conducting experiments on a direct injection, four stroke, single cylinder, water-cooled Diesel engine under fired conditions at different loads and different speeds. The formulated new heat transfer correlation is finally compared with other earlier correlations proposed by other researchers.