As a fundamental element of global measures to reduce the carbon footprint of the commercial transport and the mobile machinery and equipment sector, carbon-neutral fuels are increasingly coming into focus for heavy applications where electrification is seems to be actually not a viable option. In addition to diesel substitute fuels, alternative energy carriers like natural gas, hydrogen, methanol and ammonia are gaining increasing attention worldwide. The energy conversion of these fuels is typically taking place on the principle of premixed combustion, which places different demands on fuel injection and mixture formation, supported by proper in-cylinder charge motion and turbulence, compared to current highly optimized diesel-like combustion. Accordingly, the demand to layout multi-fuel capable engine designs centers to a high share on the above mentioned cylinder head design that can burn these different fuels with high efficiency and at the same time support a high degree of commonality with the in-series base engine in order to carry over reliable operation in all-day use and to maintain attractive production and assembly costs.
FEV Group has developed in the recent years a specific optimization tool, labeled Charge Motion Design (CMD) process, that can be effectively applied to shape intake ports and combustion chambers for such multi-fuel cylinder heads, already very early at the initial concept phase. This advanced toolchain features the capabilities to forecast and optimize the performance of different hardware arrangements and configurations for the various fuels based on condensed and simplified CFD simulations, geometric and fluidic benchmarks and other fuel specific combustion duration correlations. These correlations are tuned and calibrated to representative engine data for individual fuel types to determine the combustion characteristics, mainly regarding the main burning durations, defined by the 0-5% and the 5-50% phase, mainly by in-detail analysis of the in-cylinder aerodynamics in the combustion chamber.
This paper in hand highlights the detailed methodology application for cylinder head and combustion chamber layout and definition on the base of measurements on a state-of-the-art modular single-cylinder heavy-duty research engine. In addition to previously tuned correlations for the main low carbon/carbon-neutral fuels hydrogen, natural gas and methanol, new measurements with ammonia were used to calibrate and synchronize the correlations of the CMD process. In addition, also a dedicated variant of the external hydrogen admixture to the ammonia was also carried out on the test bench and adjusted in the CFD simulations. These fuel correlations were applied to different hardware configurations to evaluate their performance and suitability for these fuels. These configurations differed in multiple key parameters, e.g. port arrangement and layout, valve orientation and in-cylinder charge motion generation. The results of the case study are presented along with supporting single-cylinder engine measurements.
Moreover, a in-depth analysis of pent-roof and Diesel-like flat cylinder head concepts is displayed, utilizing the key findings from the CMD process and the observations from the engine testing campaign to evaluate their performance and suitability for multiple carbon-neutral fuel types. This technical study highlights the potential of CMD-driven design to enable flexible, efficient and cost-effective combustion solutions for the transition to sustainable, carbon-neutral fuels and concludes with some major optimization steps and associated achievements.