Abstract
Hydrogen fuelled engines are in the focus. They have many advantages. One of the disadvantages is the gaseous state of hydrogen at atmospheric conditions. With a gas carburettor the mixing process with the air is easy, but not accurate enough for complete control. With port injection, comparable with gasoline injection, the injector has to deliver a large volume of gas in a short time. But sequential (port) injection has more freedom in injection duration, injection pressure and the moment of injection. All these parameters can be optimized on a test rig.
This paper gives the comparison for a hydrogen fuelled single cylinder engine between a carburetted version and a sequential injection version. Mainly the indicated power output and the indicated efficiency are examined as a function of the load condition. All tests are done at a constant speed and with wide open throttle (WOT). Neglecting changes in volumetric efficiency this means that the air-fuel ratio l is inversely proportional to the power output of the engine. A hydrogen fuelled engine can thus be regulated as a diesel engine, due to the ability of hydrogen to run very lean.
For the carburetted version tests are made at different compression ratios (CFR engine with variable compression ratio) and at different ignition timings. For this engine the best compression ratio is obtained and the ignition timing is optimized as a function of the load condition. The influence of the ignition timing can be clearly explained with measured cylinder pressure diagrams (different for lean and rich mixtures). Some values are given of the influence of the compression ratio and ignition timing on the exhaust gas emissions (NO x and unburned H 2 ).
For the injected version four different geometries of the injector position (inclination of the injector against the air inlet channel) are examined. The injection parameters (timing, pressure) are experimentally analyzed. Also a CFD code (FLUENT) for the mixing process is used to understand the experimental results. So it is shown that the moment of start of injection has a significant influence on the engine characteristics.
Finally the comparison is made for the power output and the efficiency between the two versions of the engine as a function of the load condition and at optimized ignition timing. If the injector is big enough to deliver the necessary quantity of fuel in a short time (expressed in ¡ca) then with retarded injection backfire safe operation of the engine is possible.