A Review on Sustainable Diesel Engine Performance Enhancement and Emission Reduction using HHO Gas

Diesel engines is essential in transport-sector, agriculture and industry for durability and efficiency, but they are also major contributors to air pollution through emissions of CO, HC, NOₓ, PM, and CO₂. One promising solution is the use of HHO (also called oxyhydrogen or Brown’s gas), to improve combustion and reduce emissions. HHO is a stoichiometric mixture of hydrogen and oxygen produced through water electrolysis and supplied to the intake manifold to promote more complete burning of fuel. Research findings show that optimal HHO addition can improve brake thermal efficiency by 6–10%, lower brake- specific fuel consumption by 5–8%, and increase power and torque by 10–20%. Emission reductions are notable, with CO, HC, and smoke levels cut by 40–60%, though a slight rise in NOₓ has been observed under certain conditions. Advances in generation technologies, such as pulse and on-demand electrolysis, achieve higher efficiency (75–85%) compared to conventional methods. Economic studies indicate fuel savings of 5–15%, equivalent to ₹1,500–3,000 per month for medium-duty vehicles, with payback periods of 6–10 months. Despite challenges in fuel quality, infrastructure, and policy, HHO supplementation presents a sustainable, cost-effective approach to enhancing diesel engine performance while reducing environmental impact.