Investigation of a Lambda Leap Strategy for Hydrogen Internal Combustion Engines to Balance Efficiency, Performance, and Vehicle Packaging

The paper reports investigations into employing a “lambda leap” strategy for hydrogen internal combustion engines (H2ICEs), wherein inherently low NOx emissions are afforded at light load via operation at lambda 2.5 or leaner, and at higher load by operation at stoichiometry with a three-way catalyst. This approach means it is necessary under transient operation to “leap” between high values of lambda and stoichiometry from one cycle to the next, in order to avoid completely the area where high combustion NOx is generated away from lambda = 1; this is because lean catalysis of NOx will be extremely challenging there. The requirements for the cam profiles and valvetrain hardware to achieve this strategy are discussed, and a 2.0 litre in-line 4-cylinder engine configuration with the necessary valve gear functionality is modelled. The efficiency results on an operating map are then presented. In turn, this data is used to model the hydrogen consumption of two vehicles (one a saloon car and the other an SUV) on the World Light-duty Test Cycle in order to illustrate the likely improvements achieved through adoption of the strategy. The paper also explains why the strategy would be especially beneficial for light-duty H2ICEs, having as they do different habitual load operational areas compared to heavy-duty ones, and why vehicle packaging, mass, and drag advantages would accrue as well. Finally, some discussion is made regarding how H2ICEs might benefit from upsizing of their swept volumes if this strategy is successfully employed.