Untreated Exhaust Emissions of a Hydrogen-Enriched CNG Production Engine Conversion

Engine dynamometer testing was conducted on a production automotive engine. Untreated exhaust emissions were measured over a range of hydrogen/natural gas fuel mixtures and equivalence ratios (Φ).

The most important finding was that, with retarded ignition, extremely low raw NO_x emissions can be attained at the same time as high brake thermal efficiency. With a 30% hydrogen mixture and Φ = 0.65, the effect of spark timing on engine efficiency is almost negligible over approximately 15° of crankshaft rotation. For an engine load of ∼400 kPa, brake thermal efficiency remained at 30%. NOx emissions can be kept below 0.05 g/kWh for bmeps up to 500 kPa and rpms above 1700, with low hydrocarbons and minimal effect on fuel economy.