Drive Cycle Fuel Economy and Engine-Out Emissions Evaluation Using an Opposed-Piston Sleeve-Valve Engine with Lean Operation and Ignition Delay for NOx Control 2013-32-9064
In small vehicle applications in which carburetion and oxidation catalysts are used, a fuel efficient means of engine-out NOx reduction is necessary to avoid the cost of implementing a 3-way catalyst and closed-loop-controlled fuel injection system. Pinnacle Engines' single-cylinder 110cc lean-burn opposed-piston 4-stroke architecture has been tested to gather steady-state fuel consumption, emissions, and combustion stability data over a matrix of speed, load, mixture ratio, and combustion phasing. Contributions to total vehicle fuel usage and emissions production are evaluated using steady-state flow data weighted by time spent at a respective load and speed from a tested WMTC drive cycle. Cumulative emissions and fuel economy impacts are presented for multiple NOx-reducing engine control strategies using control variables of mixture ratio and combustion phasing. Pre-catalyst HC and CO levels are affected by operating strategy and are reported for catalyst load. The extent of combustion instability (COV of IMEP) required to achieve various emissions criteria is swept to evaluate what emissions regulation can be achieved with the current hardware set without NOx after treatment. Results show that operation at best efficiency mixture ratio and combustion phasing is likely sufficient to meet current emissions regulations depending on HC levels. Deviations from best efficiency mapping by a combination of leaner mixture and delayed ignition targeting minimum NOx at 6% COV of IMEP can offer Euro 4 NOx levels without after treatment. This method offers greater than 60% reduction of NOx with respect to best efficiency but is associated with less than a 1.5% fuel economy reduction.