Abstract
ABSTRACT There are many factors that affect the efficiency of NOx conversion in the diesel engine SCR (selective catalytic reduction) post-processing system. In this study, we researched the factors affecting the efficiency of NOx conversion by engine bench testing. The SCR system was applied to the Weichai WD615 engine exhaust. First, the system used DOC (Diesel Oxidation Catalyst)/DPF (Diesel Particulate Filter) of which DOC is a noble metal-containing filter, it lets the filter passes through converting nitrogen monoxide (NO) to nitrogen dioxide (NO2) for passive regenerations and to provide high hydrocarbon (HC) oxidation activity for active DPF regenerations, the DPF is a wall-flow filter used to trap the remaining soot that the DOC can not oxidize. The combined catalytic oxidation device improved the original SCR deNOx system, which we developed. The new catalytic oxidation apparatus has a simple structure and fundamentally solves the clogging problem of the SCR method and the defects led by the unstable gaseous ammonia generation. Secondly, we studied the influence of an increased urea injection on the conversion efficiency of NOx and the secondary pollution of NH3 at different speeds and torques of the engine. It was found that at the maximum removal rate, the downstream NOx concentration was only 1 ppm. The NOx conversion efficiency can reach 79.10% or more—even 99.90%. Finally, we used the KDS and the BOSCH urea injection pumps to analyze the effect of different pumps on the conversion efficiency of NOx. Hence, the matching diesel engine urea SCR post-processing system can reduce the emission concentration and pollution. There was little difference between the two pumps under most of the working conditions, although KDS was a little better than BOSCH under some individual conditions.
Highlights
Research Background Due to its high compression ratio and fuel distillation operation, diesel engines have inherent high thermal efficiency, high dynamic performance, and economic fuel efficiency (Beeck et al, 2013).While high compression ratio achieves the hightemperature ignition required, and the resulting high expansion ratio releases less heat in the exhaust emissions of the engine
A total of 6 points are set as the test points, which represented the engine running performances. They were typical emission points, of which each representative operating point is for urea injection and NOx conversion efficiency analysis based on a modified device
The pump motor runs, the urea solution in the urea tank is sucked into the pump through the liquid inlet, and the urea solution passes through the liquid pipe under the motor to reach the diaphragm of the urea pump motor (Note: the urea membrane pump = urea pump motor + diaphragm structure), with the hydraulic diaphragm reciprocating motion generated by the subsequent pipeline is pushed to the filter
Summary
Research Background Due to its high compression ratio and fuel distillation operation, diesel engines have inherent high thermal efficiency, high dynamic performance, and economic fuel efficiency (Beeck et al, 2013).While high compression ratio achieves the hightemperature ignition required, and the resulting high expansion ratio releases less heat in the exhaust emissions of the engine. Aerosol and Air Quality Research, 18: 1886–1900, 2018 particulate matter, carbon monoxide and hydrocarbons in diesel engine exhaust are becoming more stringent (Wattrus et al, 2016). It has promoted the development of efficient post-processing system of diesel engine (Johnson, 2009), exhaust gas purification technology has become the focus of research at home and abroad. At the beginning of 2010, most of the new medium and heavy diesel vehicles on major international markets, such as the US, Europe, and Japan, relied on urea-based SCR technology to meet the most stringent NOx emission regulations (Johnson, 2012). With EPA 2015 stringent management of large diesel engines for locomotives, ships and fixed generators, due to the proven performance of urea SCRs on highway and offhighway (Liu et al, 2017), the demand for NOx reduction through urea SCR catalysts is increasing (Ballinger et al, 2009; Theis, 2009; Beeck et al, 2013; He et al, 2017)
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