Reduction of Particle Number and Mass Emissions of a Modern Off-Road Diesel Engine

The oxides of nitrogen (NO_x) and particulate matter (PM) form the main challenge for diesel engine exhaust cleaning. Despite the emissions reduction, the fuel economy should be kept at a sufficient level to also prevent CO₂ increase. In the present project, a turbocharged, inter-cooled, common-rail, direct-injection, off-road diesel engine, largely used in tractors, forest machines etc., is optimized to make the engine comply with the US EPA Tier 4i/4 emissions legislation. The present study focused on pulse turbocharging and open-flow or partial diesel particulate filter system (pDPF). PM mass and PM number concentrations were determined both up- and downstream the pDPF. The engine was operated according to the steady and transient non-road emissions cycles (NRSC, Non-Road Steady Cycle; NRTC, Non-Road Transient Cycle, respectively). The main aim of the current study was to reduce PM emissions since a catalyst based on SCR technology was selected for NO_x removal. Clear benefits in PM emissions were achieved with pulse turbocharging, especially during the transient engine operation. A very slight increase in the brake specific NO_x (BSNO_x) was detected with both studied pulse manifolds while PM decreased by 20% or more. CO also decreased clearly with Pulse 1 but HC remained almost constant. The opacity peaks recorded during the NRTC measurement also decreased considerably compared with the baseline constant-pressure turbocharging. The pDPF also proved efficient both for particle number levels and PM mass. In steady-state engine operation, the DOC containing filter system removed exhaust CO and HC effectively. BSNO_x also decreased slightly. The exhaust particle number generally decreased usually the more, the larger the particles. Over the transient cycle with the pDPF, the weighed PM decreased by 77% and was clearly below the US EPA Tier 4i limit. The filter also reduced smoke opacity peaks effectively. The BSNO_x decreased more than in the steady cycle, as did CO and HC.