Exhaust Emission Control Considerations for Diesel Engines

Abstract

This chapter summarizes major recent developments in diesel emissions technologies and system design. Emissions challenges that are covered include particulate matter ( PM ) remediation using diesel particulate filters ( DPFs ), lean NO x remediation, and hydrocarbon (HC) and carbon monoxide controls. NO x control technologies are summarized, including SCR (selective catalytic reduction) with ammonia and HC‐based approaches. PM reduction technologies are evolving around new DPF materials for reduced back pressure and SCR integration, and optimization of regeneration and control. Technologies for NO x control are achieving >95% deNO x efficiency averaged over the certification test cycles. DOC (diesel oxidation catalyst) developments are used to precondition the exhaust for both deNO x and PM remediation systems and for removing unburned fuel components. They mainly involve NO oxidation to NO 2 as a function of catalyst formulation and HC oxidation parameters. Nitrous oxide ( N 2 O ) emissions are also addressed. System layout and fundamental control strategies are outlined for integrated systems involving all three unit operations.

In-Use NOx Emissions from Model Year 2010 and 2011 Heavy-Duty Diesel Engines Equipped with Aftertreatment Devices

“…The NO x emissions were elevated during the cold start for Veh-2 but a reduction in NO x emissions began once the SCR inlet exhaust reached temperatures close to 150 °C (on arterial roads). Studies have indicated that urea hydrolysis requires an exhaust temperature of at least 180–200 °C, below which the SCR efficiency falls rapidly because of cessation in urea hydrolysis. ,, Further, the optimum exhaust temperature for copper-zeolite catalyst activity that was used on Veh-2 ranges from 225 to 500 °C. , None of the SCR equipped vehicles evaluated in this study utilized technologies to generate ammonia using thermal decomposition which are shown to work at temperatures as low as 120 °C. , Given that the exhaust temperature at this stage is not sufficient for urea hydrolysis and optimum catalyst activity, it is possible that this initial reduction in NO x emissions for Veh-2 is attributable to only the EGR. The EGR valve and the SCR doser status were not collected during these experiments.…”

“…The NO x emissions profile for cold start and highway driving for Veh-3 and Veh-4 are comparable to Veh-2 (Figure b). It should be noted that both Veh-3 and Veh-4 utilized iron-zeolite SCR catalysts which have a higher activation temperature of 300 °C. ,, The major difference between these engines is clear during the latter half of the low load/slow speed industrial area driving. Unlike Veh-2 which showed an increase in NO x emissions immediately after the truck exited the highway and began driving on the industrial area loops, Veh-3 was effective in maintaining NO x reductions (Figure a) while driving on the industrial area segment (a distance of around 11 miles) for the total duration of the test.…”