A carburetted, spark ignited gasoline fuelled engine of a 5 kW rated power generator was converted to run on hydrogen. As opposed to large parts of current research, the engine conversion’s foremost goal was not to maximise efficiency and power output but rather to find a cost-effective and low-complexity conversion approach to introduce clean fuels to existing engines.
To allow for the increased volumetric fuel flow, the riser of the original carburettor was enlarged. The hydrogen flow into the venturi was metered with the help of a pressure regulator from a widely available conversion kit. The effects of different hydrogen-fuel-feed pressures on engine performance, operational stability and emission levels were examined experimentally.
It was found that the hydrogen-line pressure before startup has to be set precisely (±5 mbar) to allow for stable and emission free operation. While the rated power of the converted engine was lowered to 57% of the original’s generator, efficiency was increased by up to 9 percentage points while lowering NOx emissions drastically. In fact, under stable hydrogen supply conditions, it was shown that an average concentration of only 19 ppm NOx is feasible without any exhaust gas aftertreatment. An analytic derivation of lambda values from emission data has been examined. With a fairly constant offset of 4.3% between the measured and calculated lambda value, the stoichiometrically derived formula for lambda proved to yield precise results with little calculation effort.
As a main limiting factor for continuous low emission levels, pressure fluctuations in the hydrogen supply line were identified to strongly influence the fuel flow rate leading to inconsistent air-to-fuel ratios. Furthermore, large, abrupt reductions in engine load were identified to be critical regarding running stability and backfiring events.