Search Results

Diesel burners introduce combustion of diesel fuel to raise exhaust gas temperature to Diesel Oxidization Catalyst (DOC) light-off or Diesel Particulate Filter (DPF) regeneration conditions, thereby eliminating the need of engine measures such as post-injections. Such diesel combustion requirement nevertheless poses challenges to burner development especially in combustion control and risk mitigation of DPF material failure. In particular, burner design must satisfy good soot distribution and heat distribution at DPF front face after meeting minimum requirements of ignition, heat release, and backpressure. In burner development, Computational Fluid Dynamics (CFD) models have been developed based on commercial codes for burner thermal and flow management with capability of predicting comprehensive physical and chemical phenomena including turbulence induced mixing, fuel injection, fuel droplet transport, diesel combustion, radiation, conjugate heat transfer and etc.

2010 and future EPA regulations introduce stringent Oxides of Nitrogen (NOx) reduction targets for diesel engines. Selective Catalytic Reduction (SCR) of NOx by Urea over catalyst has become one of the main solutions to achieve these aggressive reductions. As such, urea solution is injected into the exhaust gas, evaporated and decomposed to ammonia via mixing with the hot exhaust gas before passing through an SCR catalyst. Urea mixers, in this regard, are crucial to ensure successful evaporation and mixing since its liquid state poses significant barriers, especially at low temperature conditions that incur undesired deposits. Intensive efforts have been taken toward developing such urea mixers, and multiple criteria have been derived for them, mainly including NOx reduction efficiency and uniformity. In addition, mixers must also satisfy other requirements such as low pressure drop penalty, mechanical strength, material integrity, low cost, and manufacturability.

Diesel burners recently have been used in Diesel Particulate Filter (DPF) regeneration process, in which the exhaust gas temperature is raised through the combustion process to burn off the soot particles. The feasibility of such process using the burner in large diesel applications is investigated along with a mixer and DPF. For such applications, only partial flow of the exhaust stream is fed into the burner and the resulting hot flow from combustion process is then mixed with the rest of the main stream. The amount of flow into the burner plays a vital role in overall system performance as it determines the amount of hot gas needed for Diesel Oxidation Catalyst (DOC) light-off (to facilitate DPF regeneration) and also oxygen amount needed for secondary combustion. A passive valve plate design is proposed for such flow split applications for the burner.

In order to satisfy tightening global emissions regulations, diesel truck manufacturers are striving to meet increasingly stringent Oxides of Nitrogen (NOx) reduction standards. The majority of heavy duty diesel trucks have integrated urea SCR NOx abatement strategies. To this end, aftertreatment systems need to be properly engineered to achieve high conversion efficiencies. A EuroV intent urea SCR system is evaluated and failed to meet NOx conversion targets with severe urea deposit formation. Systematic enhancements of the design have been performed to enable it to meet targets, including emission reduction efficiency via improved reagent mixing, evaporation, distribution, back pressure, and removing of urea deposits. Multiple urea mixers, injector mounting positions and various system layouts are developed and evaluated, including both CFD analysis and full scale laboratory tests.

With increasing applications of urea SCR for NOx emission reduction, improving the system performance and durability has become a high priority. A typical urea SCR system includes a urea injector, injector housing, mixer, and appropriate pipe configurations to allow continuous urea injection into the exhaust stream and evaporation of urea solution into gaseous products. Continuous operation at various conditions with high NOx reduction is possible, but one problem that threatens the life and performance of these systems is urea deposit. When urea or its byproducts become deposited on the inner surfaces of the system including walls, mixers, injector housings and substrates it can create concerns of backpressure and material deteriorations. In addition, deposits as a waste of reagents can negatively affect engine operation, emissions performance and DEF economy. Urea deposit behavior is explored in terms of heat transfer, pipe geometry, injector layout and mixing mechanisms.

The presented work evaluates several mixer designs being considered for use in large Diesel exhaust aftertreatment systems. The mixers are placed upstream of a diesel oxidation catalyst (DOC) in the exhaust system, where a liquid hydrocarbon fuel is injected. DOC exothermic behaviour resulting from each mixer at different operating conditions is evaluated. A gas flow bench equipped with a XY-Table measurement system is used to determine gas velocity, temperature, and hydrocarbon species uniformity, as well as, pressure drop. Experimental mixer data obtained from a flow bench and an engine dynamometer are compared and discussed. The experimental methodology used in this study can be used to evaluate mixers via comprehensive testing.

Selective Catalytic Reduction (SCR) based on urea water solution (UWS) has become a promising technology to reduce Nitrogen Oxides (NOx) emissions for mobile applications. However, urea may undergo incomplete evaporations, resulting in formation of solid deposits on the inner surfaces including walls and mixers, limiting the transformation of urea to ammonia and chemical reaction between NOx and ammonia. Numerous design parameters of SCR system affect the formation of urea deposits [1] ; they are: exhaust condition, injector type, injector mounting angle, geometrical configurations of mixer, injection rate and etc. Research has been available in urea deposits, mixers, urea injection rates and others [2,4,5,6]. In this paper, focus is placed on improving mixing structure design from baseline design of EU IV to EU V. On-road tests indicate that deposits are highly likely to occur near locations where spray and exhaust gas interact most.

In order to satisfy China IV (equivalent to EU IV) emission regulations, an unconventional design concept was proposed with injector closely coupled with SCR can body. The benefit of this design is that the urea decomposition pipe was removed or drastically shortened, resulting in much smaller packaging space and lower cost of the whole system. However, the resulting short urea mixing distance generates concerns on low urea mixing efficiency and risks of urea deposits. In particular, airless urea injectors tend to generate incomplete evaporation of urea water solution, resulting in high risks of urea deposits. New aftertreatment mixing structures need to be developed to resolve these technical challenges.

To satisfy China IV emissions regulations, diesel truck manufacturers are striving to meet increasingly stringent Oxides of Nitrogen (NOx) reduction standards. Heavy duty truck manufacturers demand compact urea SCR NOx abatement designs, which integrate injectors, NOx sensors and necessary components on SCR can in order to save packaging space and system cost. To achieve this goal, aftertreatment systems need to be engineered to achieve high conversion efficiencies, low back pressure, no urea deposit risks and good mechanical durability. Initially, a baseline Euro IV Urea SCR system is evaluated because of concerns on severe deposit formation. Systematic enhancements of the design have been performed to enable it to meet multiple performance targets, including emission reduction efficiency and low urea deposit risks via improved reagent mixing, evaporation, and distribution. Acoustic performance has been improved from the baseline system as well.

Refuse trucks are used in many communities for garbage collection and compression in China. This article introduces representative driving cycles of refuse trucks in multiple cities. System configuration is described first. Then, traditional pedal map, shift-pattern, and shift-point are used as basis to optimize energy utilization for specific hybrid configurations under refuse truck driving situation. Since AC power is used as source for garbage compression, to take advantage of such operating characteristics, engine start and stop technology can be a viable technology to improve fuel economy. Experiments are conducted to reach the conclusions.

Multiple suppliers have developed new cordierite 10.5″ OD substrates in China market. One key issue is to evaluate the feasibility of their applications to diesel SCR markets. To this end, test procedures were conceived and performed towards multiple substrate characteristics. Besides typical parameters such as product dimensions, structures, and material strength, thermo-mechanical properties were characterized by hot vibration, thermal shock and thermal cycle tests. Flow performance before and after tests was characterized by a hot flow bench. Four suppliers were selected to provide product samples which went through these developed rigorous test procedures. Comparisons of multiple properties were made. Conclusions regarding their applicability and recommendations for future work are provided at the end.