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This paper proposes a method of determining residual gas fraction (RGF) by sampling the CO2 concentration in the exhaust manifold of a single cylinder HSDI diesel engine. During a skip-fire event, the CO2 concentration in the exhaust gas for the last firing cycle and the subsequent motoring cycle were measured using a fast-response emissions analyzer. The ratios of these two values are shown to be indicative of the RGF. To simulate the increase in exhaust pressure found with EGR or aftertreatment systems, the exhaust back pressure was elevated using an exhaust throttle. The intake pressure was held constant over a range of engine speed and load conditions. The results demonstrate that the RGF increases linearly with increasing exhaust back pressures for all engine operating conditions.

Exhaust Gas Recirculation (EGR) is one of several technologies that are being investigated to deliver future legislative emissions targets for diesel engines. Its application requires a detailed understanding of the thermo-fluidic processes within the engine's air system. A validated Computational Fluid Dynamics (CFD) process is one way of providing this understanding. This paper describes a CFD process to analyse unsteady manifold flows and mixing fields in the presence of realistic levels of EGR. The validation methodology was drawn from the American Institute of Aeronautics and Astronautics (AIAA) and divides the problem into smaller elemental problems. Detailed knowledge about these elemental problems is easily attainable, reducing the requirement for a large number of complex validation runs. The final validated process was compared to flow visualization and particle image velocimetry (PIV) data collected from a motored engine.