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Homogeneous Charge Compression Ignition (HCCI) combustion is known for its significant fuel economy benefit with near-zero NOx and particulate emissions. Stable HCCI combustion relies on a well-controlled temperature and composition of the cylinder charge at the intake valve closing that in turn requires a precise coordination of all engine inputs. In this paper, the HCCI combustion is realized by retaining hot residual from the previous combustion event using the recompression valve strategy. The recompression valve strategy closes the exhaust valves before the top dead center and opens the intake valves at an angle symmetric to the exhaust valve closing. Depending on the engine load, different valve open/close timings with respect to the crank position are used to trap different amounts of residual gases. It is critical to coordinate the change in the valve open/close timings with the change in the injected fuel quantity during load transients in order to maintain stable combustion.

One way to achieve low temperature regeneration on diesel particulate traps is to employ NO2 as the oxidant. However, the engine may not produce sufficient NOx to achieve the required particulate regeneration. An RRT (rolling regeneration trap) was proposed as a way to enhance the effective concentration in diesel engine exhaust. The RRT uses catalyzed ceramic foam, which allows repeated use of existing NOx in the exhaust stream. The ceramic foam is a filter itself: thus, it can reduce the particulate loading on the wall-flow filter, which is more prone to plugging by the particulate deposits. Furthermore, the presence of particulate matter in the catalyzed section circumvents the high temperature limit imposed by thermodynamic equilibrium of a simple NO+NO2 +O2 system. However, experimental results revealed that the regeneration efficiency on the wall-flow section was very low and NO2 slip is an issue.

To comply with Tier II Bin 5 light-duty or 2010 heavy-duty NOx emission standards, all diesel engines require some sort of NOx control device. Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR) to reduce NOx from diesel exhaust emissions is an attractive technology for lean NOx control, especially when diesel fuel is used as the reductant. However, it has been reported that when diesel fuel is used as the reductant catalyst deactivation occurred (1). In a companion paper, we demonstrated that the HC-deactivation is caused by the mismatch of the adsorption and desorption processes of either the reactants or the products of a normal SCR reaction (2). In this paper, we probe the nature of the catalyst deactivation with various reductants. Both hydrocarbons and oxygenates were used as the reductants. The deactivation or the mismatch in adsorption and desorption rates is molecular size or chain length dependent.

The steady-state reduction of NOx at temperatures between 150-300°C has been investigated under simulated lean-burn conditions using a two-stage transient flow reactor system consisting of non-thermal plasma in combination with a sodium Y zeolite catalyst. Reactivity comparisons were made with and without plasma operation in order to identify the plasma-generated hydrocarbon species necessary for the selective catalytic reduction (SCR) of NOx. With propene as the hydrocarbon in the feed, NO is completely oxidized to NO2 in the plasma and the formation of oxidized carbon-containing species include formaldehyde, acetaldehyde, carbon monoxide, carbon dioxide, and methanol. Fourier transform infrared (FTIR) measurements indicate a close carbon balance between plasma inlet and outlet gas feed concentrations, signifying the major species have been identified.

At the current state of diesel engine technology, all diesel engines require some sort of NOx control device to comply with Tier II Bin 5 light-duty or 2010 heavy-duty NOx emission standards. Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR) to reduce NOx from diesel exhaust emissions is an attractive technology for lean NOx control, especially when diesel fuel is used as the reductant. However, it has been reported that when diesel fuel is used as the reductant catalyst deactivation occurred. Even though this kind of deactivation is reversible at high enough temperatures, it is a deficiency that needs to be overcome for the successful implementation of the technology. We studied the HC-SCR catalyst deactivation using diesel fuel as the reductant. The variables investigated included catalyst temperature, HC:NOx ratio, NOx concentration, and space velocity. The results showed that one single parameter can be used to measure the catalyst deactivation: the HC-SCR activity.

The two most common NOx reducing technologies, in an oxygen abundant exhaust stream, are urea selective catalytic reduction urea-SCR and lean NOx trap (LNT) catalysts. Each technology has advantages and disadvantages. Another selective catalytic reduction (SCR) catalyst that uses hydrocarbons (HC-SCR), specifically diesel fuel, as the reductant to reduce NOx emissions was investigated. This catalyst is a result of a high throughput discovery project and conducted in cooperation with BASF, Accelrys and funded by the Department of Energy (DOE.) Several full size 5.0L monolith catalysts were made and evaluated using a V6 turbo charged diesel engine connected to a dynamometer running light-duty transient test cycles. The NOx efficiency on the HWYFET and US06 tests were measured to be 92% and 76% respectively. The FTP was 60% on a weighted basis.

A unique silver/alumina selective catalytic reduction (SCR) catalyst which used hydrocarbons (HC-SCR) to reduce NOx emissions was investigated. Diesel fuel or ethanol were used as the reductants to evaluate catalyst performance. Several full size 5.0L monolith 2.0 and 3.0 wt.% Ag2O-Al2O3 catalysts were created. Testing was conducted using a 6.6L Duramax turbocharged heavy duty diesel engine. Dynamometer testing on the heavy duty FTP and SET 13 transient test cycles was conducted. The NOx conversion efficiency was evaluated as a function of catalyst volume, inlet cone angle, hydrocarbon to NOx ratio (HC:NOx), and space velocity. Oxygen effects on the NOx reaction and the HC slip past the HC-SCR catalyst were also determined. An FTIR was used to evaluate unregulated emissions. Testing on the heavy duty FTP and SET 13 test cycles, with diesel fuel as the reductant, resulted in a 60% and 65% NOx conversion reduction respectively.

The performance of a commercial Cu-zeolite SCR catalyst after differing degrees of hydrothermal aging (aged for 72 hours at 500, 700 and 800°C with 10% moisture balanced with air) was studied by spatially resolving different key reactions using gas-phase FTIR measurements. Gases were sampled along a channel at different positions and analyzed using FTIR, which overcomes the interference of water and nitrogen on ammonia concentration detection encountered in standard mass spectrometer-based spatial resolution measurements. The NO:NO₂ concentration ratio was changed so that the standard (NO:NO₂ = 1:0), fast (NO:NO₂ = 1:1) and NO₂ (NO:NO₂ = 0:1) SCR reactions could be investigated as a function of the catalyst's hydrothermal aging extent. In addition, the effects of hydrothermal aging on the activity of NH₃ and NO oxidation were also investigated. Hydrothermal aging had little effect on NO oxidation activity.

A unique catalyst developed using high-throughput discovery techniques in collaboration with BASF Corporation and Accelrys, Inc. was investigated at General Motors under simulated diesel engine exhaust feed conditions for the selective catalytic reduction of NOx. A hydrocarbon mixture was used as the reductant to model the multi-component nature of diesel fuel and the catalyst was evaluated over a wide range of temperatures (150 - 550°C) relevant to light-duty diesel exhaust. This report investigates the effects of NOx (as NO or NO2), hydrocarbon concentration level (HC:NOx ratio), oxygen concentration, NO concentration, catalyst space velocity, catalyst temperature, and the co-presence of hydrogen on steady-state NOx reduction activity. Using these results, a control strategy was developed to maximize NOx conversion over the wide-ranging exhaust conditions likely to be encountered in light-duty diesel applications.

Unique silver/alumina (Ag-Al₂O₃) catalysts developed using high-throughput discovery techniques in collaboration with BASF Corporation were investigated at General Motors Corporation under simulated lean-burn engine exhaust feed conditions for the selective catalytic reduction of NOx using hydrocarbons (HC-SCR). Hydrocarbon mixtures were used as the reductant to model the multi-component nature of diesel fuel and gasoline. Previous work has shown promising HC-SCR results in both laboratory reactor and engine dynamometer testing. This report investigates several aspects of HC-SCR catalyst durability, including thermal durability, sulfur tolerance, and hydrocarbon deactivation.

A procedure has been developed to build system level predictive models that incorporate physical laws as well as information derived from experimental data. In particular a soot model was developed, trained and tested using experimental data. It was seen that the model could fit available experimental data given sufficient training time. Future accuracy on data points not encountered during training was estimated and seen to be good. The approach relies on the physical phenomena predicted by an existing system level phenomenological soot model coupled with ‘weights’ which use experimental data to adjust the predicted physical sub-model parameters to fit the data. This approach has developed from attempts at incorporating physical phenomena into neural networks for predicting emissions. Model training uses neural network training concepts.