Further significant CO 2 emission reduction beyond 2020 is mandatory in the United States and might also become mandatory in Europe, depending on the passenger car CO 2 legislation, which is to be enacted. Hybrid and plug-in hybrid vehicles might account for a big portion of these CO 2 reductions as a consequence of the favourable current legislative treatment which does not associate CO 2 emissions from electric power generation with vehicle CO 2 emissions. Nevertheless, these powertrains benefit from a highly efficient combustion engine. Exhaust heat recovery poses new synergetic possibilities for technologies to mitigate knock like cooled external exhaust gas recirculation and condensed water injection. The condensed water injection concept, which is proposed in this article, demonstrates a potential for efficiency increase of 3.3%-3.8% in the region of the minimum specific fuel consumption on a stoichiometric combustion concept with Miller cycle and cooled external exhaust gas recirculation. Further improvement of the efficiency of up to 16% is possible at full-load operation. If water injection is used in addition to homogeneous lean combustion, an efficiency gain of 4.5% in the region of the minimum specific fuel consumption is achieved.

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