Hydrogen enriched natural gas as fuel for CHP units

Abstract

This study investigates the potential benefits and drawbacks of adding hydrogen to natural
gas grids on stationary cogeneration plants. Fuel blended with up to 30% hydrogen by
volume was tested using a commercial six-cylinder spark ignition engine designed for pure
natural gas operation without modifications to the engine. In line with normal practice for
cogeneration plant engines, the power output, the lower heating value of the air/fuel
mixture, the ignition timing and the engine speed were held constant. Results show that
increasing hydrogen concentration led to an earlier peak cylinder pressure, indicating
significantly accelerated combustion. As a result, peak pressures were up to 39% higher
than with natural gas and up to 10% of fuel burned before top dead center. Despite this,
thermal efficiency improved up to 6%. Cycle-by-cycle variation decreased by half, indi-
cating reduced misfires on account of hydrogen. However, nitrogen oxide emissions
increased exponentially with increasing hydrogen amounts. Our findings suggest that
hydrogen-enriched natural gas is a promising fuel for stationary cogeneration plants, but
modifications to engine control settings are necessary to ensure optimal performance and
compliance with nitrogen oxide emission regulations. These modifications might include
adjustments to the mixture control system and ignition timing.

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