Clean Technology 2010

Cylinder Pressure, Heat Release, Specific Heat Ratio and Duration of Combustion for Spark Ignition Engine

M.S. Shehata
Benha University, EG

Keywords: cylinder pressure, heat released, duration of combustion, entropy


Cylinder Pressure, Heat Release, Specific Heat Ratio and Duration of Combustion for Spark Ignition Engine M. S. Shehata Assistant Professor Mechanical Engineering Technology Department Higher Institute of technology Banha University, Egypt Abstract Experimental study are carried out for investigating cylinder pressure, performance parameters, heat release, specific heat ratio and duration of combustion for multi cylinder spark ignition engine. Cylinder pressure is measured for Gasoline, Kerosene and Liquefied Petroleum Gases (LPG) separately as a fuel for spark ignition engine at different engine speeds. The engine is coupled by water dynamotor for measuring engine brake power. Fast Fourier Transformations (FFT) are used for transforming measured cylinder pressure from time domain to frequency domain. Empirical correlation is carried out for calculating cylinder pressure in frequency domain at different engine speeds. Inverse Fast Fourier Transformations (IFFT) are used for reconstructing cylinder pressure in time domain. Good agreement between reconstructed and measured cylinder pressure are obtained for different engine speeds. First law-single zone model with specific heat ratio temperature dependence γ(T) are used for calculating heat release and heat transfer to cylinder wall. Logarithmic scale of measured cylinder pressure and calculated volume are used for determining polytropic index of compression and expansion processes. Third order correlation for γ(T) is obtained which is in a good agreement with other researchers. Position of maximum cylinder pressure, maximum temperature and maximum heat release are determined and arrangement respectively for different engine speeds. Duration of combustion (Start/end of combustion) for different engine speeds are determined using four different methods: (i) Fuel burned mass fraction, (ii) Change of entropy, (iii) Specific heat ratio temperature dependence, and (vi) Change of pressure versus cylinder volume in the logarithmic scale. Using entropy change for determining duration of combustion is simple and accurate method. Measurement of engine cylinder pressure is useful tool for understanding the combustion characteristics and determination of reliable statistical data that cannot measured directly. This study is contributed in determining combustion characteristics for different fuels, development and finding optimal operating conditions of multi cylinders spark ignition engines. Key Words (Cylinder pressure, heat released, duration of combustion, entropy)
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