Trade-offs between engine performance and emissions in diesel engines fueled with hydrogen from ammonia cracking and biodiesel blends

In this study, hydrogen gas produced from ammonia cracking was used as the secondary fuel in an unmodified diesel engine, and the effects of using 20 % microalgal-based biodiesel blends along with hydrogen on combustion, performance, and emissions were examined. Hydrogen was injected at liters per minute (LPM) into the intake manifold at three different flow rates of 10 LPM, 15 LPM, and 20 LPM. The flow rates were managed by the rotameter, and flashback arrestors were used to avoid backfire. The hydrogen-enriched biodiesel blends enhanced in-cylinder pressure and heat release rate, improving combustion efficiency in the diesel engine. The high cetane number and oxygen content of biodiesel contributed to complete combustion; hydrogen's high flame speed shortened combustion duration and enhanced brake thermal efficiency, particularly in the blend with 20 % biodiesel and hydrogen. The addition of hydrogen at 20 LPM increased the brake thermal efficiency by 23.08 % compared to diesel, while brake specific fuel consumption decreased to 0.36 kg/kWh. Hydrocarbon and carbon monoxide emissions were reduced by 12.6 % and 50 %, respectively at stoichiometric conditions. However, NOx emissions increased by up to 3.4 % due to high combustion temperatures. The combustion duration was reduced by 17.65 %, and peak in-cylinder pressure increases from 32 bar for diesel to 55 bar with hydrogen-enriched blends. The equivalence ratio of 1.1 further reduced emissions but slightly decreased thermal efficiency due to dilution effects.