One of the important inputs to a spark ignition engine which affects nearly all engine outputs is spark advance. Spark advance not only affects fuel efficiency and exhaust emissions but is also a factor in the tendency for detonation or engine knock. Increasing pressure for reduction of emissions and better fuel economy is making effective spark advance control more important. The desire for improved efficiency is complicated by the increased use of low octane, lead-free gasoline which is an influence toward conservative, inefficient engine designs for reduction of engine knock. Conventional spark advance systems control on parameters which are inputs to the combustion process, such as manifold vacuum and engine speed. This paper describes a microprocessor based spark timing controller based on measurements of cylinder pressure history, a parameter which is a result of the combustion process. To feedback element is an experimental piezoelectric pressure transducer of an inexpensive design which would be suitable for mass production. Results are presented showing that this feedback controller is able to control spark advance to 1 percent of optimum even over fuel-air ratio changes of 40 percent. The controller also effectively controls engine knock to levels which are not harmful.

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