Internal combustion engines (ICEs) still have significant potential for efficiency improvements and emissions reductions, potentially exceeding diesel-like efficiencies in the medium term with technologies like gasoline compression ignition (GCI). Combined with other strategies like hybridisation and lightweighting, fuel consumption in light-duty vehicles could be reduced by 50% compared to the current average, while exhaust pollutants can be controlled to levels well below current legislation.

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This paper provides a comprehensive overview of the current state and future potential of internal combustion engines, highlighting the significant scope for improving their efficiency and reducing their environmental impact. The analysis is well-structured and supported by data, although there is some reliance on projections and estimates. The discussion of various technologies and their implications is insightful and balanced. Overall, this is a strong and valuable contribution to the field.