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A major problem with making accurate cylinder pressure measurements using piezoelectric pressure transducers in IC engines is thermal shock. This affects most derived parameters although the greatest error is in the indicated mean effective pressure (IMEP), which can be affected by over 10%. In this paper, thermal shock has been quantified for a wide range of engine conditions. Thermal shock was found to be most significant at low engine speeds, high loads and advanced ignition timings. A good correlation between thermal shock and peak pressure has been established for Kistler 6123 and 6125 transducers when dealing with cycle averaged data. This resulted in the development of a numerical thermal shock correction routine which was used for all subsequent data processing. Use of this improved analysis software demonstrated that the error in the calculated IMEP was significantly improved for the Ford Zetec engine tested.

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.

This paper addresses issues associated with the accurate determination of gross heat release energy. The magnitude of analysis and measurement errors has been quantified using simulated and measured gasoline engine pressure data. This has revealed that calculated gross heat release is very sensitive to the assumed ratio of specific heats, charge to wall heat transfer and pressure data errors. Two improved heat release models have been proposed and further investigated and shown to generally give good performance for specific applications although further work is required to fully quantify their accuracy.

The effect of crank angle (CA) resolution on the analysed cylinder pressure data has been investigated using both simulated and experimental engine cylinder pressure data. This revealed that the noise levels in some of the derived parameter data can be greatly increased by low ADC and high CA resolutions. A method for reducing the noise spikes by dynamically adjusting the calculation CA resolution at each point in the engine cycle is proposed and shown to be very effective. The accuracy of the calculated imeps has also been studied using experimental pressure data. The sensitivity to both CA resolution and integration period phasing was found to be small. Overall, this work has shown that the best CA resolution to use depends on the application. A CA resolution of 0.5° to 1.0° should be most suitable for a compression ignition engine increasing to 1.0° to 2.0° for most spark ignition engine studies.