The objective of this project is to develop a model of an automotive catalytic converter that is based on unsteady flow theory, rather than the steady flow assumptions that are traditionally used in the majority of existing catalyst models. Steady flow models cannot simulate the propagation of pressure waves through the catalyst channels and so they cannot be integrated with commercially available engine simulation packages, all of which track the movement of pressure waves throughout the entire engine in order to calculate the true mass flow of gas into and out of the cylinder.
The catalyst acts as an abrupt area change in the exhaust system and therefore reflects waves generated by the strong blowdown pulses back to the exhaust valves. In addition to affecting the flow of exhaust gas from the cylinder, and hence engine performance, these reflected pulses also cause variations in the composition of the exhaust gas and therefore the reaction rates within the catalyst. The true performance of both the engine and the catalyst can therefore only be predicted when both are linked together within the same one-dimensional unsteady flow simulation.
The first phase of model validation was performed using data recorded from a single-pulse test rig which allowed the propagation of waves to be studied in isolation from the effects of temperature gradients and interference from the oppositely moving waves that occur on a running engine. Pressure wave profiles were recorded at various points of the system using high-speed transducers and data-logging equipment.
The second validation phase used data recorded from a four-cylinder, 1.8-litre, four-stroke, naturally-aspirated gasoline engine. Taken from a Nissan Almera (model year 2002), this engine incorporates a number of advanced emissions control features, including intake swirl control plates, variable valve timing (VVT) on the intake, exhaust gas recirculation (EGR), and a close-coupled three-way catalyst (TWC).
Photo of test engine used in catalyst validation tests
Schematic of test engine showing location of measurement transducers
1. McCullough, G. , Douglas, R., Spence, S., Cunningham, G., McMackin, M., Foley, F. ‘An Experimental and Predictive Evaluation of Unsteady Gas Flow through Automotive Catalyst Elements’. SAE Paper No. 2005-01-3134. SAE Journal of Fuels and Lubricants, pp 1186-1197, ISBN 0-7680-1690-8, 2005.
2. McMackin, M., McCullough, G., McDowell, A. P. N., ‘Simulation of the Unsteady Gas Flow through a Three-way Automotive Catalyst: A Preliminary Study’ SAE Paper No – 2005-01-2216. SAE Journal of Fuels and Lubricants, pp 1175-1185, ISBN 0-7680-1690-8, Sept 2005.
3. M. McMackin, G. McCullough , A.P.N. McDowell, ‘Computer Simulation of the Performance of a 1.8 Litre Gasoline Automotive Engine’, Proc of VAFSEP Conference, Dublin City University, Ireland . 6-9 July 2004, Pg 345-350. ISBN 1 872327 47 8
The authors gratefully acknowledge the Engineering and Physical Sciences Research Council (EPSRC) for funding the project ( GR/S18007/01) , Calsonic Kansei for supplying the production automotive engines and exhaust systems, and Optimum Power Technology for providing the VIRTUAL 4-STROKE software.