Robert Albert Stein

Comparison of Dual Retard VCT to Continuously Variable Event Valvetrain

Variable cam timing strategies which utilize retard of the intake and exhaust valve events at part load have been previously shown to provide improved fuel consumption and feedgas NOx. These benefits can be increased by enhancing the combustion system with variable charge motion. A variable event duration valvetrain was simulated on engine dynamometer by running a series of short duration/low lift intake valve events. The fuel consumption benefit for this simulated variable event valvetrain is compared to that of dual retard VCT with variable charge motion. An estimated upper limit for the fuel consumption improvement potential of variable valve timing is presented. This upper limit includes both pumping work reduction and indicated efficiency improvement with high levels of exhaust residual dilution. The measured benefits of dual retard VCT and of the variable event valvetrain are compared to the estimated upper limit.

A New Analysis Method for Accurate Accounting of IC Engine Pumping Work and Indicated Work

In order to improve fuel economy, engine manufacturers are investigating various technologies that reduce pumping work in spark ignition engines. Current cylinder pressure analysis methods do not allow valid comparison of pumping work reduction strategies. Existing methods neglect valve timing effects which occur during the expansion and compression strokes, but are actually part of the gas exchange process. These additional pumping work contributions become more significant when evaluating non-standard valve timing concepts. This paper outlines a new analysis method for calculating the pumping work and indicated work of a 4-stroke internal combustion engine. Corrections to PMEP and IMEP are introduced which allow the valid comparison of pumping work and indicated efficiency between engines with different pumping work reduction strategies. Several example data sets are presented which illustrate the method and the necessity for the corrections when analyzing engines with non-standard valve timings. The upper limit potential improvement in BSFC available from PMEP reduction is presented and compared to the actual benefit obtained with three pumping work reduction strategies: 1) variable valve timing, 2) intake charge dilution (stratified lean operation) and 3) cylinder deactivation.

The Effects of Load Control with Port Throttling at Idle- Measurements and Analyses

This paper describes an experimental and analytical study conducted to investigate the effects of load control with port throttling on stability and fuel consumption at idle. With port throttling, the pressure in the intake port increases during the valve-closed period due to flow past the throttle. If the pressure in the port recovers to ambient before the valve overlap period, back flow into the intake system from the cylinder is eliminated. This allows increased valve overlap to be used without increasing the residual mass fraction in the cylinder.

Effect of Thermal Strain on Measurement of Cylinder Pressure

Cyclical exposure of a piezoelectric transducer to high temperature gas results in an error in the measured pressure due to thermal strain of the transducer diaphragm. Thermal strain results in a decrease in the measured values of IMEP and PMEP, while burn times calculated using the method of Rassweiler and Withrow are relatively unaffected. The severity of the effect can be minimized by coating the transducer diaphragm with RTV. When the effects of thermal strain persist into the intake stroke, a method of detection at low speed is to overlay and compare the firing and motoring intake stroke pressure traces.