The oxides of nitrogen (NOx) 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 NOx 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 NOx (BSNOx) 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. BSNOx 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 BSNOx decreased more than in the steady cycle, as did CO and HC.

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