Comparing emissions of a propane engine at various speeds and loads

A study was undertaken to determine the emission characteristics of a 4.2 L 2003 Ford ESG-642 propane engine. The engine was operated at 63 combinations of speeds and loads while exhaust gases were measured. The first objective was to determine the best operating load and speed combination to minimize emissions of CO and HC+NOx (in g/hp-hr). Significant differences were only found between loaded and non-loaded test settings. The second objective was to compare the measured emissions with California Air Resource Board (CARB) certification levels for the same model engine. CARB certification levels for CO emissions were met at 2200, 2400 and 3000 rpm at 100% load and certification levels for the combination of HC+NOx were only met at 2400 rpm at 100% load.