Strategies for enhanced after-treatment performance: Post injection characterization and long breathing with low NOx combustion

A novel long breathing technique was created to achieve ultra-low NO x emissions with reduced supplemental fuel consumption compared to conventional strategies. Long breathing refers to the use of in-cylinder NOx reduction to prolong the NOx storage (breathing) cycle of a lean NOx trap (LNT). Exhaust gas recirculation (EGR) was used with conventional diesel fuel and steady-state experimental tests identified that engine-out NOx emissions of 0.4 to 0.8 g/kW˙hr were suitable for long breathing operation. The results indicated that the reduced engine-out NOx emissions significantly prolonged the NOx storage cycle and decreased the supplemental fuel consumption penalty of the LNT for all of the tested conditions.;However, the long breathing strategy was mainly suitable for low and medium loads, below 10 bar indicated mean effective pressure (IMEP), because the supplemental fuel savings of the long breathing LNT were offset by increased fuel consumption from the engine and increased smoke emissions at higher loads. Long breathing was also developed with neat n-butanol for in-cylinder NO x reduction. However, the long breathing strategy with neat n-butanol was primarily suitable for low load operation (below 6 bar IMEP) under the tested conditions because of increased engine fuel consumption and increased NOx emissions at higher loads.;Post injection strategies were developed for active control of the exhaust gas temperature for enhanced LNT performance. The results indicated that active management of the exhaust gas temperature was achieved by using relatively high intake oxygen, 16.5 to 20.8 percent by volume (%V), and by controlling the duration of early post injections, 20 to 60 degrees crank angle after top dead centre (°CA ATDC). Post injection strategies were also implemented for increased in-cylinder production of desirable NOx reducing agents like hydrogen to benefit the LNT NOx conversion efficiency. Engine tests demonstrated that the combination of very low intake oxygen (<10%V), low temperature combustion, and an early post injection exponentially increased the yields of hydrogen (0.76%V), carbon moNOxide (1.96%V), and ethylene (0.19%V) despite the relatively low in-cylinder temperatures. However, the same conditions also undesirably increased the methane emissions up to 0.30%V.