Engine combustion pressure

May 14, 2016

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The cylinder head gasket with integrated combustion pressure sensors (CHGICPS) reported here targets advanced engine controls and in particular those based on the HCCI, PCCI, or LTC combustion principles, for gasoline, diesel, and alternative fuel engines. Due to the fiber optic combustion pressure sensor's (CPS) accuracy at low pressure during compression integrated into the CHGICPS, this device aims at in-cylinder prediction of mass air flow as well as in-cycle closed loop control of pilot fuel injection in a diesel engine. This paper reports on a replaceable CPS which allows installation and removal from the cylinder head gasket (CHG) without the need for removing the engine head. At the same time the distance layer thickness of CHGICPS is minimized to 2.5 mm and 3.4 mm, depending on the access ability and space constraints around coolant and lubrication ports in the engine. A multilayer steel CHGICPS prototype is constructed with replaceable fiber optic combustion pressure sensors (CPS) that operate on the principle of modulation of light reflected from a metal diaphragm deflecting under effect of cylinder pressure. The signal conditioners are remotely located from the CHGICPS in the tested design. The initial test results of the combustion pressure measurement CHICPS demonstrated high fidelity pressure traces at low and high engine speeds for various throttle positions for the CPS using a heat shield as compared to a recessed and exposed fiber-optic CPS. The difference between the reference sensor and the fiber-optic CPS is less than 0.1 bar during compression below 5 bar and .5 bar for a cylinder pressure range from 0 to 50 bar. The fiber-optic CPS removal and installation was performed successfully on the engine without removing the head with no signs of observable leakage. The measured pressure difference error between reference sensor and the fiber-optic sensor at peak power 2900 rpm and wide open throttle (170 bar peak cylinder pressure) shows a 2.3% error as compared to the water cooled reference sensor. Calibration adjustment of the fiber-optic CPS is shown to improve this performance. Future design considerations for integrating the signal conditioners into the CHGICPS and improved sensor performance are discussed. Overall, combining the pressure performance capabilities of a replaceable fiber-optic CPS that does not require removing the engine head, the suitability of the CHG location for all engine types, and the economic advantages of design simplicity, makes the CHGICPS a viable solution for combustion control technology in the future.

Source: papers.sae.org
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