Experimental Studies of Low-Load Limit in a Stoichiometric Micro-Pilot Diesel Natural Gas Engine

While operating at light loads, diesel pilot-ignited natural gas engines with lean premixed suffer from poor combustion efficiency and high methane emissions. This work investigates the limits of low-load operation for a micro-pilot engine that uses stoichiometric mixture to enable nitrogen oxide emission control. By optimizing hardware, conditions, injection strategies, this study focused on defining lowest achievable load while maintaining equivalence ratio acceptable stability. A multi-cylinder 6.7 L was converted run premix maximum contribution 10%. With base compression 17.3:1, intake manifold pressure limit 80 kPa(absolute). At reduced 15:1, increased 85 kPa, raising minimum stable load. Retarding phasing, typically used in spark-ignition achieve lower also tested but found be limited by degraded ignition later timings. Reducing pilot improved stability, as did increasing quantity cost substitution ratios. The further NOx hydrocarbon loads below practical dual-fuel limit, transition will likely required corresponding implications aftertreatment system.