Numerical Simulation of Hydrogen Combustion in a Wankel Engine

With the modern push for sustainable energy and transportation, new and old technologies are being developed to reduce emissions and increase efficiency. In this domain, Wankel engines are seeing a resurgence, as their compact size and power density makes them an attractive choice for range extenders in electric vehicles. One of the main setbacks of Wankel engines is the poor combustion efficiency due to unburnt pockets of fuel, combustion chamber leakage and high heat transfer losses.

Using a 3D, transient CFD combustion analysis of a 5cc Wankel engine, this thesis looks to exploit pure hydrogen fuel properties as a method for reducing the volume of the unburnt pocket, as hydrogen flame speeds are much higher than those from traditional fuels. Different values of air-fuel equivalence ratio (λ) are simulated to find the ideal ratio that combines a high flame speed with low NOx emissions. The λ = 1.4 case produces the highest work of any hydrogen case. However, it also produces a significant amount of NOx compared to leaner operating conditions. The power output of hydrogen remains lower than that of iso-octane (gasoline), however the λ = 1.8 hydrogen case shows comparable thermal efficiency, and much lower NOx emissions than the iso-octane.