Hydrogen Jet Ignition - a pragmatic approach to zero engine out emissions in future heavy duty vehicles

点击翻译按钮获取中文摘要

Traditional heavy duty IC engines utilise liquid or gaseous hydrocarbon fuels, with only c.35% of the energy in the fuel converted in to useful work. The by-products of combustion include soot and NOx, both harmful to health. Significant attention is now being paid to zero tailpipe emission electric vehicles. However, recent life cycle analysis has shown it can take up to 10 years to break even in terms of equivalent CO2 to a modern diesel engine in a family sized passenger car (with considerable CO2 associated with battery production). The IC engine costs approximately 10% the capital cost of an electric powertrain for such a passenger car. In trucks the outlook is staggering, with battery costs of several hundreds of thousands of US dollars in the Tesla Semi. Fuel cells provide an alternative but cannot yet sustain the required degree of transient operation. We propose a radical new solution that involves the use of a new type of IC engine combustion system fuelled with hydrogen and capable of converting over 50% of the energy in the fuel in to useful work. The combustion system is based upon an insulated turbulent pre-chamber independently fuelled with hydrogen. When fuelled with fast burning hydrogen (fast even under ultra lean conditions) this system can result in zero tailpipe emissions of NOx and soot under all conditions. An illustration of the combustion system is shown. The reaction jets enable increased flame area and hence rapid combustion under ultra lean fuel conditions. The hydrogen can either be stored directly on-board or reformed from hydrogen-rich carriers, e.g. liquefied synthetic-fuels or ammonia, with the 'cold energy' of the liquefied fuel recaptured to further improve engine cycle thermal efficiency. Compared to fuel cell electric vehicles the system can be operated under more transient driving conditions (one of the remaining stumbling blocks to fuel cells). Simpler pre-chambers are currently used in Formula 1 without a separate fuel injector in the pre-chamber (meaning the fuelling rates in the pre and main chambers cannot be independently optimised, which is key to ultra lean and high efficiency operation). When coupled to exhaust heat recovery we believe an overall powertrain efficiency of 55-60% will be feasible, which is competitive with fuel cell efficiency for significantly lower cost.