The mainstream automotive market is rapidly transitioning to electrified and fully electric powertrains. Where gasoline engines are still employed, they are frequently turbocharged units with relatively low maximum engine speed and modest power density. The hypercar class, in contrast, has recently seen somewhat of a renaissance in high performance, high speed, naturally aspirated gasoline engines, which are prized for their emotional contribution to the vehicle.
In order to guarantee high conversion efficiency of a Three Way Catalyst in the exhaust system, an engine must be operated at stoichiometric air-fuel ratio. At high power density, this may result in very high exhaust gas temperature, which poses a risk to engine and vehicle hardware. A number of technological interventions to extend the maximum stoichiometric performance whilst respecting component limitations have already been described in the literature, but many of these are not applicable to specific engine architectures in the hypercar niche.
This work describes some of the unique challenges for such vehicle types in achieving stoichiometric operation in all conditions and identifies water injection as a key enabling technology. An experimental campaign on a high speed normally aspirated mule engine with water injectors installed in the intake ports is described. This is supported by Computational Fluid Dynamics calculations with detailed chemistry and bench testing of the injectors using Phase Doppler Anemometry and momentum flux techniques. It is shown that stoichiometry can be maintained at peak power, but some further complementary technologies may be of interest to limit water consumption and ensure an adequate combustion stability.