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This paper addresses issues associated with the accurate determination of absolute cylinder pressure in internal combustion engines. Pressure referencing errors are shown to produce large errors in derived parameters such as polytropic index, mass fraction burned and charge temperature. Two alternative pressure correction methods, namely inlet manifold pressure and polytropic index referencing are investigated in detail. Sources of errors and algorithm improvements are investigated and discussed. Comparison between the two pressure referencing techniques is made using measured cylinder pressure data obtained from a gasoline engine operating over a wide range of speeds and loads. The analysis shows that both of the methods should be capable of referencing typical experimental pressure data to within +-100 mbar. The work has demonstrated that accurate absolute pressure referencing can only be achieved if common pressure measurement errors are minimised.

This paper addresses issues associated with the measurement and analysis of crank angle based cylinder pressure to obtain accurate knock data. Issues examined include knock model features, the effect of sample size, the impact of sampling frequency, optimum knock windowing and the influence of transducer in-cylinder location and mounting arrangement. The study has demonstrated that a very large sample size is required to obtain good repeatability and at least 1000 engine cycles is recommended for knock intensity determination. A knock window of TDC to TDC+40 degrees has been shown to be appropriate whilst a 0.2 degree crank angle resolution is considered to be adequate for the knock algorithm employed. This work has also confirmed that transducers should have high natural frequency, be flush mounted to avoid cavity resonance and that knock signals can be significantly influenced by transducer location.