Study of the behaviour of an exhaust gas heat exchanger for improved engine warm-up

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Study of the behaviour of an exhaust gas heat exchanger for improved engine warm-up

Burke, R.D. / Brace, C.J. / Akehurst, S. / Pegg, I. / Stark, R.

Because of the many short distance journeys undertaken by vehicles, engine cold-start is a target for significant fuel consumption benefits. By reducing the warm-up time, engine friction losses can be reduced and cabin heating can be provided sooner. This can be achieved by increasing the available thermal energy per unit thermal mass. In this paper the effects of a heat exchanger are investigated to use otherwise waste heat from exhaust gases. The device was installed in the coolant circuit of a 2.4 L Diesel engine and experiments were conducted over 25 °C-start New European Drive cycle. The system offered a small oil and coolant warm-up benefit of 1 - 4 °C over phase 1 of the drive cycle. However, this improved warm-up was not reflected in benefits in fuel consumption. The limited impact on engine performance was a result of the increased thermal inertia required to integrate the heat exchanger into the system. The benefits are strongly dependent on engine duty cycle and it was estimated that to achieve a significant improvement in oil warm-up rate an additional thermal mass of less than 1 kg water should be the design target.