Hydrogen fuelling of an internal combustion engine
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis traces and critically reviews recent developments in hydrogen fuelling of internal combustion engines. It reports the development of an improved fuelling system that has been tested on a Ricardo E6 variable compression spark ignition engine, in the Thermodynamics laboratory, Department of Mechanical Engineering at the University of Canterbury. The introduction of hydrogen to an internal combustion engine via the inlet manifold (external mixture formation), often results in the occurrence of pre-ignition. This is because hydrogen, with its low ignition energy and extreme lean limit of flammability, is easily ignited by residual gases or hot spots in an engine cylinder. If pre-ignition occurs before inlet valve closure, the mixture may burn back through pre-mixed gases in the inlet manifold. Another serious disadvantage with external mixture formation is that hydrogen displaces a large volume of air, effectively reducing the volumetric efficiency of the engine. To overcome these problems hydrogen may be injected directly into an engine combustion chamber during the compression stroke, although if injection commences too early in the stroke pre-ignition may still occur. It is thus considered that the most desirable system for fuelling an internal combustion engine on hydrogen is to employ direct gaseous injection at high pressure late in the compression stroke. There are a number of problems involved with the design and development of a suitable high pressure hydrogen direct injector. In particular the injector must actuate rapidly and be controllable to a high degree of accuracy to consistently meter precise quantities of fuel at each injection. Leakage of hydrogen through the injector when closed must be minimised in order to avoid unnecessary fuel wastage and to prevent the build up of a flammable pre-mixed mixture that could lead to pre-ignition. A suitable injector has been designed and tested. The injector is electromagnetically actuated for electronic control of injection timing and duration (control of injection duration being necessary to vary the quantity of fuel delivered). The injector has a nominal lift distance of 0.2 mm and can be opened for durations as short as 1 ms. A fluorocarbon elastomer Quad-ring was used in the seat of the valve to provide a leak free seal for the high pressure hydrogen. Engine testing was conducted to determine the performance of the valve. The engine was tested on hydrogen for compression ratios of 8:1, 10:1 and 12:1 over a range of operating conditions. Results of engine performance, complete with combustion chamber pressure traces and exhaust gas emission analysis are presented. The design concept has proven to be successful with satisfactory operation of the engine on hydrogen without any combustion related problems. The elastomeric seal, although providing leak free operation, had an average lifetime of about 30 minutes. Future injector development work should focus on devising a highly durable injector seat seal which minimises leakage.