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, indicating 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.