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Dynamic Diesel Engine Timing with Microwaves—The General Motors Approach
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Abstract
Conventional production methods for setting initial pump timing in indirect injection diesel engines are subject to tolerance stack-up errors which contribute to vehicle-to-vehicle variations in tailpipe emissions and smoke levels. This problem has been addressed through the development of a new dynamic timing apparatus in which injection pump timing adjustments are made under hot-test conditions. The new timing apparatus employs microwave sensing of the combustion chamber to determine the dynamic piston top dead center (TDC) of a cylinder to within ±0.1° crankangle. Furthermore, the onset of prechamber luminosity, rather than injector needle motion, is used as the signal to be timed. This signal is abrupt, readily detectable and more directly related to engine performance than is start of injection. Both the microwave and luminosity sensing functions are integrated into a single probe which is used in place of a glow plug.
Experimental results which illustrate the accuracy of the location of TDC by microwaves and the dependence of prechamber luminosity on engine operating conditions are given. In addition, data are presented which indicate that the dynamic timing method can significantly reduce the initial timing related vehicle-to-vehicle variation of exhaust emissions. The production implementations of this timing system by Chevrolet and Oldsmobile are also described.
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Krage, M., Lienesch, J., and Violetta, D., "Dynamic Diesel Engine Timing with Microwaves—The General Motors Approach," SAE Technical Paper 820053, 1982, https://doi.org/10.4271/820053.Also In
References
- Lienesch, J. H. Krage, M. K. “Using Microwaves to Phase Cylinder Pressure to Crankshaft Position,” SAE Trans. 88 410 418
- U.S. Patent Application.
- Talder, R. W. GM Research Laboratories, personal communication
- Hess, T. Salzgeber, D. “The Stanadyne DB2 Distributor Pump for Medium Duty Diesels,” SAE Paper No. 790899 , presented at the Off-Highway Vehicle Meeting and Exposition, MECCA, Milwaukee 1979
- Howes, P. “The New CAV Microjector Injector,” SAE Paper No. 800509 , presented at the 1980 Congress and Exposition 1980
- Reilly, D. J. “The New GM 6.2 Liter V-8 Diesel Engine -- Designed by Chevrolet,” presented at this Congress