Identification of the errors related to the estimation of the actual combustion rate of the fuel from the measured cylinder pressure of di diesel engines

Abstract

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.

As recognized by various researchers the most important source of information for a reciprocating internal combustion engine is the cylinder pressure diagram. Its validity for direct injection (DI) diesel engines is extremely important since the engineer can estimate and understand the effect of various operating or design parameters on the combustion mechanism. But, since the measured cylinder pressure diagram is the result of various thermo-physical processes taking place inside the combustion chamber it cannot provide direct information concerning the combustion rate of fuel. For this reason techniques have been developed to estimate the rate at which energy is released inside the combustion chamber by processing the cylinder pressure diagram. These techniques are referred to as "Heat Release Rate Analysis" and are used to estimate the combustion rate of fuel inside the combustion chamber. During its estimation various errors may arise due to either the cylinder pressure measurement or inadequate description of the various mechanisms, i.e. heat transfer etc. In the present investigation the heat release rate estimation procedure is analyzed at the fundamental level using a detailed simulation model and available experimental data. A source of error is indicated that is higher compared to any of the conventional ones. From the anal is, it is shown that it is not possible to estimate the actual rate of heat release inside the combustion chamber of DI diesel engines from the measured cylinder pressure trace using existing heat release rate analysis techniques even if all mechanisms are described accurately. From the employment of the simulation technique the actual source of this error is revealed.