Search Results

Many Diesel engine development programs concentrate almost exclusively on steady state investigations to benchmark an engines performance. In reality, the inter-action of an engine's sub-systems under transient evaluation is very different from that evident during steady state evaluation. The transient operation of a complete engine system is complex, and collecting test data is very demanding, requiring sophisticated facilities for both control and measurement. This paper highlights the essential characteristics of a Diesel engine when undertaking testbed transient manouevres. Results from simple transient sequences typical of on-road operation are presented. The tests demonstrate how transient behaviour of the engine deviates greatly from the steady state optimum settings used to control the engine.

The use of variable geometry turbocharging (VGT) as an aid to performance enhancement has been the subject of much interest for use in high-speed, light-duty automotive diesel applications in recent times (4). One of the key benefits anticipated is the improved transient response possible with such a device over the conventional fixed geometry turbine with wastegate. The transient responses of two different types of variable geometry turbocharger have been investigated on a dynamic engine test bed. To demonstrate the effect of the turbocharger on the entire system a series of step changes in engine load at constant engine speed were carried out with the turbocharger and exhaust gas recirculation (EGR) systems under the control of the engine management microprocessor. Results are presented which compare the different performance and emissions characteristics of the devices. Some control issues are discussed with a view to improving the transient response of both types.