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Compressed Natural Gas (CNG) engines have become a promising alternative to classical IC engines because of low pollutant and carbon dioxide emissions. This paper will first briefly summarize these advantages and then concentrate on the modeling and the control of CNG engines. In the modeling part, it will be shown which effects are similar to those observed in gasoline SI engines and what new sub-models are necessary. In the control part, the problem of sudden A/F ratio changes (for instance during the regeneration of NOx trap catalysts) will be considered. In order to avoid excessive NOx engine-out emission in these transients it is important to switch from lean to rich conditions within very few combustion cycles while keeping the engine torque constant (for comfort reasons). The paper presents a model of the most important phenomena associated with those transients and a feedforward control that meets the mentioned requirements.

This paper describes an investigation of implementing variable valve timing with the use of a secondary valve in the intake tract The secondary valve acts in series with the conventional poppet valve of the engine, which is actuated in the conventional manner and with fixed timing It is significantly easier to adjust the timing of the secondary valve than that of the main valve There are two possible modes of operation of this device One is to control valve overlap, improving low speed low load performance The other is to use it as a load control mechanism, replacing the conventional throttle and therefore reducing the ‘pumping losses’ associated with conventional throttling We have implemented such a system on a motored single-cylinder research engine using pneumatic actuation Our experiments have demonstrated successful load control, significant pumping loss reduction, and control of backflow from the exhaust to the intake manifold

This paper describes an investigation of a method of implementing VVT with the use of a secondary valve in series with the conventional intake valve of the engine. The secondary valve is not required to withstand the temperatures and pressures of combustion, and therefore can be of relatively lightweight design, so that it is easier to adjust the timing of the secondary valve than that of the main valve. Experiments with such a valve installed in a production engine indicate that benefits of variable valve timing such as overlap optimisation and throttleless load control (4% Fuel benefits at 980 rpm and 1.5 bar IMEP) are attainable with this system.

This paper presents a control-oriented mean-value model of a pressure wave supercharger (PWS) which is coupled to an SI-engine. The model is able to predict the engine's intake pressure and other main process variables. The model is validated by stationary and transient measurements on an engine dynamometer.