Combustion Studies for PFI Hydrogen IC Engines

摘要

Interest in alternative fuels is motivated by concerns for greenhouse gas accumulation, air quality, security of energy supply and of course the non-stop increasing crude oil and natural gas prices. Hydrogen usage can be a solution for these problems. Hydrogen plays the role of an energy carrier that has two major advantages: it can be generated from many sources and it is very clean in its use. One end-use technology that can handle hydrogen is the well-known internal combustion engine (ICE). However, before this technology can be put to use, it needs to be able to compete with conventionally fuelled power units. Particularly in terms of specific power output and NO{sub}x emissions, development work needs to be done. In the work described in this paper the main focus is on the combustion strategies for high efficiency and low NO{sub}x emissions. A comparison is made between lean burn and EGR (exhaust gas recirculation) strategies. Using stoichiometric mixtures with EGR and the use of a three-way catalyst, very low NO{sub}x emissions are obtained. To increase the power output boosting the inlet charge is a possibility. Different system setups have been studied and finally a combination is proposed of EGR and the boosting process by feeding the exhaust gas to the intake of a supercharger. The experiments are carried out on two single-cylinder engines, a low-speed CFR engine and a high-speed prototype Audi engine. These engines are optimized for hydrogen use (ignition and injection timings). Pressure measurements have been conducted on the CFR engine for different air-fuel ratios and for different compression ratios, and on the Audi engine over a wide range of engine load conditions (n = 1500 to 4000 rpm and λ = 1,25 to 3,25) to create a database for validation of simulation models. The influence of the ignition timing on the torque (MBT strategy) and NO{sub}x emissions is examined and the effects of late ignition (after TDC) are analyzed in detail with the pressure curves.