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The current publication considers the benefits of placing a SCR system upstream of the DOC. This will enable rapid light-off of the upstream system. The tradeoff between engine out NOx levels, exhaust temperature, and dosing levels between upstream and downstream SCR will be compared with respect to achieving below 0.05 g/hp-hr NOx over the composite FTP and RMC. NOx conversion efficiency will also be compared with respect to N2O formation and NH3 slip.

As vehicle emissions regulations become increasingly stringent, there is a growing need to accurately model aftertreatment systems to aid in the development of ultra-low NOx vehicles. Common solutions to this problem include the development of complex chemical models or expansive neural networks. This paper aims to present the development process of a simpler Selective Catalytic Reduction (SCR) conversion efficiency Simulink model for the purposes of modeling tail pipe NOx emission levels based on various inputs, temperature shifts and SCR locations, arrangements and/or sizes in the system. The main objective is to utilize this model to predict tail pipe NOx emissions of the EPA Federal Test Procedures for heavy-duty vehicles. The model presented within is focused exclusively on heavy-duty application compression ignition engines and their corresponding aftertreatment setups.

Current legislative trends regarding diesel emissions are striving to achieve two seemingly competing goals: simultaneously lowering NOx and greenhouse gas (GHG) emissions. These two goals are considered at odds since lower GHG emissions (e.g. CO2) is achieved via high combustion efficiency that result in higher engine out NOx emissions and lower exhaust gas temperatures [1, 2]. Conversely, NOx reduction technologies such as SCR require temperatures above 200°C for dosing the reductant (DEF) [3, 4, 5] as well as for high conversion efficiencies [1, 2, 6, 7, 8, 9]. Dosing DEF requires injection pressures around 5 bar to ensure proper penetration into the exhaust stream as well as generate the appropriate spray pattern and droplet sizes. Dosing DEF generally requires long mixing and/or high turbulence (high restriction) areas so that the aqueous urea solution can be converted into gaseous NH3 without deposit formation [8, 10, 11, 12, 13, 14, 15].

Tighter emission norms and fuel economy demands have prompted diesel engine manufacturers to implement Aftertreatment systems for both light-duty and heavy-duty diesel applications. After implementing Diesel Particulate Filter (DPF) technology to comply with 2007 Environmental Protection Agency (EPA) emissions regulations, OEMs have turned their attention towards NOx reductions with SCR technology. Current SCR technologies include liquid based Urea injection into the exhaust stream for NOx reductions and Solid Ammonia Storage and Delivery System (ASDS) which involves dosing gaseous Ammonia. Irrespective of the technology in use, the estimation of engine-out NOx emissions plays a vital role in reductant (Urea/Ammonia) dosing estimation via feed-back controls. The general method for determination of the engine-out NOx emissions is to use commonly available NOx emission sensors (NOx Sensors). However, NOx sensors have their own drawbacks.

With the emission norms becoming more and more stringent along with the focus on reducing ownership and operating costs, the need to optimize the aftertreatment system becomes much more evident. Thus, the well monitored, optimized usage of urea or ammonia (NH₃) for the NOx reduction in an SCR system is critical to reduce the operating cost of the vehicles and to comply with emission regulations. In Ammonia Storage and Delivery System (ASDS), pure gaseous NH₃ from the NH₃ cartridges is being used for the reduction of the engine-out NOx in the exhaust stream over the NPF (NOx Particulate Filter). In almost all NOx reduction systems, NOx sensors play an important role in determining the amount of urea or NH₃ to be dosed for efficient NOx reduction with minimal NH₃ consumption and slippage for best possible fluid economy.

An integrated system model containing sub-models for a multi-cylinder diesel engine, NOx and soot(PM) emissions, diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) has been developed to simulate the engine and aftertreatment systems at transient engine operating conditions. The objective of this work is two-fold; ensure correct implementation of the integrated system level model and apply the integrated model to understand the fuel economy trade-off for various DPF regeneration strategies. The current study focuses on a 1.9L turbocharged diesel engine and its exhaust system. The engine model was built in GT-Power and validated against experimental data at full-load conditions. The DPF model is calibrated for the current engine application by matching the clean DPF pressure drop for different mass flow rates. Load, boost pressure, speed and EGR controllers are tuned and linked with the current engine model.

Heavy-duty diesel engine particulate matter (PM) emissions must be reduced from 0.1 to 0.01 grams per brake horsepower-hour by 2007 due to EPA regulations [1]. A catalyzed particulate filter (CPF) is used to capture PM in the exhaust stream, but as PM accumulates in the CPF, exhaust flow is restricted resulting in reduced horsepower and increased fuel consumption. PM must therefore be burned off, referred to as CPF regeneration. Unfortunately, nominal exhaust temperatures are not always high enough to cause stable self-regeneration when needed. One promising method for active CPF regeneration is to inject fuel into the exhaust stream upstream of an oxidation catalytic converter (OCC). The chemical energy released during the oxidation of the fuel in the OCC raises the exhaust temperature and allows regeneration.