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Increasing the number of cold-start engine cycles which could be run in any one day would greatly improve the productivity of an engine test facility. However with the introduction of forced cooling procedures there is the inherent risk that test-to-test repeatability will be affected. Therefore an investigation into the effects caused by forced cooling on fuel consumption and the temperature distribution through the engine and fluids is essential. Testing was completed on a 2.4 litre diesel engine running a cold NEDC. The test facility utilises a basic ventilation system, which draws in external ambient air, which is forced past the engine and then drawn out of the cell. This can be supplemented with the use of a spot cooling fan. The forced cool down resulted in a much quicker cool down which was further reduced with spot cooling, in the region of 25% reduction.

The measurement of vehicle modal emissions is technically challenging due to the major issue of determining exhaust gas mass flow rate and ensuring that it is synchronous with the emission measurement of that corresponding ‘slug’ of exhaust gas. This is very evident when attempting to measure small passive NOx catalyst conversion efficiencies. This paper highlights alignment issues with regard to the variation of time delays associated with engine and vehicle events and the CO2 tracer method for determining exhaust gas flows.

Time-alignment sensitivity studies have been carried out to assess the accuracy of instantaneous mass NOx emissions on a chassis rolls dynamometer. The work is part of a larger project aimed at measuring passive NOx catalyst conversion efficiencies. Instantaneous NOx emissions are examined in relation to the NEDC vehicle speed trace at multi sampling points, and phase and time alignment issues are highlighted and discussed. It has been found that a small mismatch of the vehicle speed trace to the instantaneous mass of emissions of ± 2 seconds can lead to results indicating that the conversion efficiency is anywhere between 0-20%. Finally, examples are presented showing the difficulties of attempting to adjust the time alignment of raw emissions data.

An experimental study has been carried out to assess the capability of injecting vaporised fuel into the exhaust gas of a diesel engine to achieve elevated outlet temperatures from an oxidation catalyst for the thermal regeneration of particulate filters. Termed catalytic combustion and passive in nature, controlled experiments have proved the concept with the limitation on catalyst outlet temperature being dictated by the material limits of the exhaust system and the availability of oxygen.

Currently, 80% of European diesel passenger cars are turbocharged and as emission standards become more stringent exhaust gas recirculation (EGR) will be the primary means of suppressing oxides of nitrogen (NOx). The lighter the load the greater will be the combustion tolerance to increased EGR flow rates and hence increased NOx suppression. Automotive diesel engines using wastegated turbochargers cannot recirculate above 50% EGR without some sort of “added” device or system, which is able to displace the inlet fresh air charge. This has been demonstrated by throttling the diesel intake to reduce the fresh air inlet manifold pressure so allowing more EGR flow by virtue of a higher exhaust-side pressure due the effects of the turbocharger. The method reported here investigates a different approach to increasing the EGR rates by replacing a fixed geometry turbocharger (FGT) with a variable geometry turbocharger, (VGT).

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.