Multifuel CHP HCCI Engine towards Flexible Power-to-fuel: Numerical Study of Operating Range

Abstract The transition towards 100% renewable electricity production already raises several challenges at only 20-30% of renewable share. To match energy production and consumption, there will be a need for massive daily and seasonal electricity storage, in particular for fluctuating sources such as wind and solar. Power-to-fuel is one of the energy storage systems that allows long term storage such as season shifting. Electricity can be stored into fuels that are gaseous (hydrogen or methane), easily liquefiable (ammonia), or liquid (methanol). Still, these four fuels are regarded separately in terms of energy production, which reduces the flexibility of the power-to-fuel technology and its potential use as a storage mean. Our approach is to integrate these four fuels into a single technology for power and heat production: Homogeneous-Charge Compression-Ignition (HCCI) engines. Therefore, we developed a 0-Dimensional model to assess the suitability of a unique HCCI engine for the combustion of the four fuels of interest. This paper reports the feasibility of compression-ignition within achievable intake conditions (temperature and pressure) for various engine compression ratios, equivalence ratios and exhaust gas recirculation rates. For the four fuels, we obtained a proper ignition within a single engine design and for intake conditions (temperature and pressure) that can be sustained by recovering the heat losses of the engine only. As a consequence, power-to-fuel can effectively be used as a storage system when combined to a multifuel HCCI engine for the fuel reconversion to energy. Yet the low power densities estimated require further work on increased equivalence ratio and boosting conditions, as well as on the ringing risks associated with such techniques.