Browse Publications Technical Papers 2019-24-0194

A Mild Hybrid SIDI Turbo Passenger Car Engine with Rankine Waste Heat Recovery 2019-24-0194

In the strive for more fuel-efficient vehicles all possible measures are considered to increase the efficiency of the combustion engine. 48V mild hybrid technology is one such measure; SIDI (Spark Ignited Direct Injection) engines with Miller technology another, while recovering energy from the engine waste heat (WHR) is yet an option to increase fuel conversion efficiency. Here, for the first time, we will publish the results from an advanced engineering project at Volvo Cars including all these components. We have successfully built an ethanol based Rankine system around a 4-cylinder, 2.0 litre SIDI-engine, including 48V mild hybrid technology. The Rankine system uses the engine exhaust as heat source, while the expansion of the ethanol steam occurs in an axial piston expander coupled both electrically to the hybrid system and mechanically to the engine crankshaft. This dual power output from the steam expander we see is of particular importance for a passenger car with transient driving style, giving the opportunity to recover more energy from the waste heat by overcoming the slow response from the steam system with the fast response of the electrical hybrid system. First initial results on the engine bench indicate a remarkable decrease in brake specific fuel consumption, with fuel conversion efficiency well above 40% for the combined system, operating the engine at stoichiometric conditions with full emission compliance, while the combined powertrain system gives advantages in both city (mild hybrid), rural (optimized engine, WHR) and highway conditions (WHR). A detailed description of the system will be given in the paper and presentation, including the sophisticated dedicated control system of the Rankine cycle, but also showing the challenges we faced building and testing the Rankine based WHR system.


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