Aftertreatment System Research Articles

Electric Heater for Rapid Heating of the Exhaust Gas Aftertreatment System

Electric Heater for Rapid Heating of the Exhaust Gas Aftertreatment System

Experimental mild conversion of a lean burn natural gas engine with SCR to a hydrogen engine: NOx and GWP potential for marine applications

Emissions of nitrogen oxides (NOx) from marine propulsion systems have gained public interest resulting in emission limits as defined by the International Maritime Organization (IMO) with IMO Tier III, especially for vessels operating in Emission Control Areas (ECA). The reduction of greenhouse gas emissions is also increasingly important for marine propulsion. Minimizing NOx while reducing climate impact calls for technologies such as the gas engine with aftertreatment systems, preferably with the ability to run on alternative fuels. A proven technology for reducing NOx in marine engines is the Selective Catalytic Reduction (SCR) aftertreatment system. It is also possible to avoid engine raw emissions by shifting the combustion process to lower temperature levels. Hydrogen is an alternative fuel with combustion properties enabling premixed operation at significantly higher air-fuel ratio than natural gas (NG) and thus, reducing raw NOx emissions. The study uses a systematic approach to compare emissions and efficiency of a lean-burn gas engine with a natural gas and a mild conversion hydrogen setup, utilizing two different strategies: combustion of NG with the assumption of an SCR catalyst and high raw NOx emissions and combustion of pure hydrogen using the NOx reduction potential of higher excess air. The scope of the study makes it possible to illustrate engine concepts for future applications in the displacement class of 4.8 L per cylinder. The highest efficiency of 45.3% was achieved with the natural gas engine and SCR. The concept with the lowest Global Warming Potential (GWP) was the hydrogen fueled engine under the prerequisite of using green hydrogen, accompanied by a reduction in efficiency of 0.6% compared to the efficiency optimum of NG with SCR. Assuming the use of gray hydrogen, the GWP was 48% and 52% higher than with NG and NG with SCR, respectively, at the efficiency-optimal operating points.

Meeting future NOX emissions using an electric heater in an advanced aftertreatment system

Engine and aftertreatment solutions are being identified to meet the upcoming ultra-low NOx regulations on heavy duty vehicles as published by the California Air Resources Board (CARB) and proposed by the United States Environmental Protection Agency (US EPA) for the year 2027 and beyond. These standards will require changes to current conventional aftertreatment systems for dealing with low exhaust temperature scenarios. One approach to meeting this challenge is to supply additional heat from the engine; however, this comes with a fuel penalty which is not attractive and encourages other options. Another method is to supply external generated heat directly to the aftertreatment system. The following work focuses on the later approach by maintaining the production engine calibration and coupling this with an Electric Heater (EH) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) followed by a primary aftertreatment system containing a downstream Selective Catalytic Reduction (SCR). External heat is supplied to the aftertreatment system using an EH to reduce the Tailpipe (TP) NOx emissions with minimal fuel penalty. Two configurations have been implemented, the first is a Close Coupled (CC) LO-SCR configuration and the second is an Underfloor (UF) LO-SCR configuration. The CC LO-SCR configuration shows the best outcome as it is closer to the engine, helping it achieve the required temperature with lower EH power while the UF LO-SCR configurations addresses the real-world packaging options for the LO-SCR. This work shows that a 7 kW EH upstream of a LO-SCR, in the absence of heated Diesel Exhaust Fluid (DEF), followed by a primary aftertreatment system met the 2027 NOx regulatory limit. It also shows that the sub-6-inch diameter EH with negligible pressure drop can be easily packaged into the future aftertreatment system.

Experimental and numerical investigation on the urea-deposit formation at different severities in selective catalytic reduction systems

Complex Exhaust Aftertreatment System (EATS) designs with Selective Catalytic Reduction (SCR) system can suffer deposit problems due to the liquid film formation in critical regions. Experimentally validated numerical prediction methods can help detect these problematic areas to eliminate deposit formation problems in product development and ongoing product development stages of EATS. This study investigates the spray-wall interaction, the liquid film formation at different severities, the liquid film evaporation by injecting Urea Water Solution (UWS) into an impingement plate in a non-uniform flow medium under different operating conditions, experimentally and numerically. The experimental set-up includes a backward facing step flow through an impingement plate. During experiments, after a specified time, the UWS injection was stopped, and a non-uniform liquid film evaporation due to non-uniform flow was also investigated, separately. Experimental and finite volume based numerical studies show that the liquid film layer formed in the stagnant flow regions has greater risks in terms of deposit formation than the other regions in an EATS. The wall cooling occurred mostly on the spray footprint portion of the impingement plate due to the liquid film formation during UWS injection, the liquid film in this part was rapidly evaporated after UWS injection was stopped and no deposit formation was observed in this part for each case under study. Experimental and numerical studies show that deposit formation occurred in the stagnant regions where the liquid film did not evaporate. The numerical results agree well with the experimental results and they demonstrate the predictive capability of the numerical model for the deposit formation.

The influence of sodium on the catalytic properties, low-temperature hydrothermal stability, and sulfur resistance of Cu-SAPO-34 for NOx reduction by NH3-SCR

In the actual diesel vehicle after-treatment systems, Cu-SAPO-34 selective catalytic reduction (SCR) of NOx catalyst simultaneously experiences the failure of sodium (Na) poisoning, low-temperature hydrothermal (LTH) deactivation and SO2 poisoning. This work investigated that the Na-loaded Cu-SAPO-34 catalysts were severally subjected to LTH treatment and sulfur poisoning for the first time. Our characterizations revealed that Na played entirely different roles in above two scenarios. In the LTH process, Na readily exchanges the protons of Si-OH-Al moieties on the zeolite framework, which inhibits the hydrolysis of the framework and further restrains the formation of SCR-inactive species. However, for SO2 poisoning, the presence of Na accelerates the deactivation of Cu-SAPO-34 because more stable sulfate species are formed on the catalyst, which severely block the pores and reduce the active sites. It is expected that these results could assist the design of SCR catalysts to meet ultra-low NOx emission.

Future HD Diesel and Hydrogen-Fueled Concepts: Emissions Challenges and System Solutions

<div class="section abstract"><div class="htmlview paragraph">Future heavy-duty (HD) concepts should fulfill very tight tail-pipe NO<sub>x</sub> emissions and simultaneously fulfill the fuel efficiency targets. In current HD Euro VII discussions, real working cycles become key to ensure emission conformity. For instance, cold start and cold ambient conditions during testing with low load profiles starting from 0% payload, require external heating measures. Knowing the trade-off between fuel consumption and tail-pipe NO<sub>x</sub> emissions a holistic engine and EAT system optimization with innovative thermal management is required.</div><div class="htmlview paragraph">Towards a carbon neutral mobility, Hydrogen combustion engines are one of the key solutions. Advanced combustion system development enables maximal usage of lean burning as the major advantage of the Hydrogen fuel for efficiency improvement and NO<sub>x</sub> reduction. Considering future NO<sub>x</sub> regulations in real-world working cycles, an efficient exhaust after-treatment (EAT) system which is well optimized to the air-path and the Hydrogen combustion characteristics is required.</div><div class="htmlview paragraph">In this paper, a systematic investigation is carried out by means of the model-based holistic approach. The target is an optimization of both engine and EAT layout, including advanced thermal management for future HD concepts. Both Diesel and Hydrogen HD concepts are investigated.</div><div class="htmlview paragraph">The model-based emission conception is based on both the conventional WHTC cycle as well as on selected real field cycles. Close-coupled dual-stage SCR with twin dosing is considered with multiple system layouts in order to minimize the Diesel engine fuel penalty during the heat up phases. A comparison between the emission behavior and after-treatment systems of Diesel and Hydrogen engines is performed.</div><div class="htmlview paragraph">In addition, external EAT heating such as electric heated catalyst is investigated for Diesel applications and the potentials regarding CO<sub>2</sub> emissions compared to conventional engine-based thermal management measures are shown.</div><div class="htmlview paragraph">The optimized system layout for both Diesel and Hydrogen HD concepts are compared, especially for the EAT technology and layout. As outlook, future potentials and optimization possibilities for combustion systems and future emission reduction technologies are described.</div></div>

Impact of a Commercially Available Low Carbon Renewable Diesel Fuel on the Light-Off and Light-Down Characteristics of a Diesel Oxidation Catalyst.

Meeting future greenhouse gas emissions targets in transportation may require transition in part to renewable low carbon fuels to power the medium- and heavy-duty sectors. At this moment, market renewable low carbon diesel fuels are available and integrated with the fueling infrastructure in select areas. Though this is encouraging, little is known about the impact these renewable diesel fuels may have on modern aftertreatment systems and their ability to convert toxic emissions. This work explores the impact of a renewable hydrotreated vegetable oil (HVO) diesel fuel on catalyst light-off and light-down of a diesel oxidation catalyst (DOC) with a production diesel engine over ramp rates reflective of real-world operation. Hydrocarbon (HC) and carbon monoxide (CO) emissions were investigated using various exhaust analyzing instruments placed before and after the model γ-Al2O3 DOC: Flame ionization detector (FID), nondispersive infrared (NDIR), and Fourier transform infrared spectroscopy (FTIR). The results of this work conclude that HC and CO conversion during catalyst light-off and light-down is significantly impacted by the fuel properties unique to the mostly paraffinic renewable HVO diesel, with light-off and light-down of the catalyst being improved for the renewable diesel fuel with respect to a certification diesel fuel for all ramp rates explored. Compared to certification diesel, HVO diesel reduced steady-state DOC-out HC and CO at idle by >50% and reduced the 50% conversion temperature (T50) during light-off by 45 °C for both HC and CO at a 20 °C/min ramp rate.

Experimental study on transient emissions characteristics of a heavy duty natural gas engine under world harmonized transient cycle

In this study, the transient emissions characteristics under WHTC for both cases with and without an aftertreatment system (AS) were investigated. The engine operating parameters were measured to reveal the factors influencing the emissions. The effects of engine thermal state (the oil temperature, coolant temperature and exhaust temperature) on emissions and AS were analyzed. The results show that emissions under WHTC are influenced by engine operating conditions and are higher in the cold start test. The CO emissions are sensitive to changes in the excess air coefficient. The NOx emissions are highly consistent with changes in the engine throttle values. The HC emissions are almost dominated by variations of the engine torque at high speeds. In addition, the exhaust temperature has a significant impact on AS performance. The conversion efficiencies of CO, NOx, and HC in the cold start test are respectively 95.8%, 97.5%, and 88.3%, while those of CO, NOx, and HC in the hot start test are respectively 98.4%, 99%, and 99.1%. Overall, the CNG engine with AS can meet the China VI emission limits and even more stringent emission standards in the future. This study provides a reference for exploring methods of emission reduction for CNG engines.

Applying 3D X-ray Microscopy to Model Coated Gasoline Particulate Filters under Practical Driving Conditions.

Recent progress in 3D X-ray microscopy allows the analysis of coated gasoline particulate filters on a detailed pore-scale level. However, derivable detailed three-dimensional models for filter simulation are not applicable under transient driving conditions of automotive aftertreatment systems due to their inherent complexity. Here, we present a novel concept to utilize highly resolved 3D X-ray microscopy scans and their quantitative analysis for a macroscopic model of coated gasoline particulate filters intended to be applied in a driving cycle. A previously developed filtration model build on a 1D + 1D flow model on the channel scale of a filter is utilized. Accompanying measurements conducted on a dynamic engine test bench serve as validation for pressure drop and filtration characteristics. With the determined properties from 3D X-ray microscopy, the macroscopic model successfully replicates the measurements. Regarding the filter coating, the reduced porosity and a decrease of medium sized pores relative to an uncoated substrate reduce the filtration efficiency under steady-state as well as transient conditions.

The effect of ammonia gas and UWS injection on the N2O formation in diesel engine after-treatment systems under steady and transient conditions

In this study, the N2O emission formation from heavy-duty diesel engine was studied by injecting ammonia gas and urea water solution (UWS) in Cu-zeolite SCR. Furthermore, the effect of exhaust gas temperature and NH3/NOx (α) ratio on the N2O formation were investigated. The ammonia was supplied using an ammonium carbamate (AC) based ammonia generating system. Experiments were performed under the European stationary cycle (ESC), world harmonized transient cycle (WHTC), and non-road transient cycle (NRTC). Ammonia gas injection produced a higher amount of tailpipe N2O than UWS injection for all test conditions. Compared with UWS an increment of 27% in N2O formation for ammonia gas was observed during the ESC test. The N2O emissions of ammonia gas injection in the WHTC and NRTC were increased compared with that of UWS during the cold phase by 63% and 55%, respectively, and during the hot phase by 57% and 74%, respectively. Meanwhile, NO and NO2 emissions were decreased by injecting ammonia gas compared with UWS. The higher NH3/NOx (α) ratio led to higher tailpipe N2O and lower NO and NO2 emissions. For each reductant test, the concentration of N2O formation was high at the exhaust gas temperature of 200–250 °C. These presented results provide useful information about the N2O formation from after-treatment systems of diesel engines when ammonia gas is used.

The impacts from cold start and road grade on real-world emissions and fuel consumption of gasoline, diesel and hybrid-electric light-duty passenger vehicles

Progressively stringent regulations regarding vehicle emissions and fuel economy have spurred technology diversification in light-duty passenger vehicles (LDPVs). To assess the real-world emissions and fuel economy performances of hybrid electric vehicles (HEVs) compared to conventional internal combustion engine (ICE) vehicles, on-road measurements of ten gasoline, four diesel and six full hybrid LDPVs were performed using portable emissions measurement systems (PEMS) in Macao, China. The hot-running emission results indicate that the high emission risks of gasoline vehicles are associated with high mileage and old model years. Diesel vehicles are found to be the highest pollutant emitters in this study due to the intentional removal of aftertreatment systems. Under hot-running conditions, HEVs, as expected, could achieve carbon-reduction benefits of approximately 30 % (i.e., lower CO2 emissions and fuel consumption) compared to their conventional gasoline counterparts, while no measurable reduction in pollutant emissions was observed except in NOX (~70 % reduction). In contrast, the cold-start extra emissions (CSEEs) of CO2 reached 120–364 g/start for these HEVs, even exceeding the maximum values of conventional gasoline vehicles. However, the higher CO2 CSEEs of HEVs can be far offset by their hot-running emission reduction benefits. For tailpipe pollutants, the CSEEs of the HEVs were reduced by 21 %–68 % on average in comparison to those of conventional gasoline vehicles. Furthermore, strong correlations (R2 values of 0.69–0.89) between the road grades and relative emissions were observed. These results can provide necessary information regarding the improvement of future LDPV emission models and inventories.

Effect of mixer structure on liquid film formation and NOx conversion efficiency in Selective Catalytic Reduction system

Selective Catalytic Reduction as an efficient technology to reduce NOx emission has been widely applied in exhaust aftertreatment system. However, the reductant injection causes inevitable impingement on the exhaust pipe and mixer surface and the liquid film will be generated. In this paper, the simulation of a double-blade mixer (Mixer 1) is verified by a bench test and other three kinds of mixer structures (baffle mixer: Mixer 2, blade-baffle mixer: Mixer 3, and blade mixer: Mixer 4) are simulated. The effect of the mixer structures on the liquid film formation, the pressure drop, the flow and temperature distribution after the mixers and ultimately the NOx conversion efficiency are investigated. Results show that the liquid film is prone to form and accumulate at the connection region between the mixer and exhaust pipe, and liquid film tends to develop with the flow direction. Mixer 2 and Mixer 4 shows smaller liquid film area about 15 cm2. The temperature distribution in four types of mixers shows negligible difference (within 4 °C). And NH3 mass fraction distribution uniformity and pressure drop show a trade-off relationship. For the vertical injection system, it is found Mixer 3 gets the worst NOx conversion efficiency, 57%, and Mixer 2 shows better NOx conversion efficiency, 78%.

Experimental analysis of engine out emissions of a light-duty diesel engine during warm-up under cold start conditions

Emission targets of diesel engines are achieved by high-performance exhaust gas aftertreatment systems (EATS). Due to the light-off temperature, the system does not work as desired under cold operating conditions. This is especially challenging with the introduction of Euro 7 because engine warm up is getting more critical, as not only emission limits are getting tighter, but also the range of ambient temperatures is widened. Especially cold start conditions will be challenging: On one hand engine out emissions cannot be converted by the EATS before light-off which is extended by a greater temperature deficit. On the other hand, engine out emissions are affected by poor combustion boundary conditions. This paper focuses on the impact of temperature on emission formation by carrying out the first five km of three different driving cycles under cold start conditions. Based on these cycles, representative stationary operating points for each emission species were defined. A method was developed to reproduce thermal boundary conditions from engine warm up. This method allows to investigate the impact of thermal conditions on emission formation in steady state. Therefore a light-duty diesel engine was instrumented with a high number of temperature sensors in the cylinder liner wall and cylinder head as well as in the oil, gas, fuel and coolant path. The results were analyzed using 0D/1D simulation models to isolate the thermal impact on the emission formation. The obtained results serve as a basis for following measures on a similar single-cylinder research engine to develop innovative cold start measures.

Optimal control of real driving emissions

Real driving emissions (RDE) testing is an important legislative tool to reduce the gap between type-approval and real-world emissions of internal combustion engines. Since low fuel consumption and low nitrogen oxides (NOx) emissions are conflicting objectives, the setpoints of a Diesel engine and its exhaust-gas aftertreatment system have to be optimised and controlled accordingly. To this end, several authors have developed a so-called supervisory controller. In order to comply with RDE legislation, most approaches use a conservative tuning and thus sacrifice performance. In this paper, we explicitly include the RDE requirements in the optimal control problem, which we then solve using direct multiple shooting and nonlinear programming. Using the optimal solution as a benchmark and comparing it to a conservative strategy, we find that fuel savings of up to 3% are possible in simulation. Furthermore, as a first step towards an online, RDE compliant, and optimal supervisory controller, we use Pontryagin’s minimum principle to derive the fact that the optimal costate related to the tailpipe NOx emissions is piecewise constant.

The impact of thermal status on emissions of a non-road diesel engine equipped with aftertreatment system under transient operation

The current study investigates the influence of hot and cold start on the emissions of a non-road diesel engine with an after-treatment system. The emissions were studied by experimental measurements on an engine during non-road transient operating conditions. These results indicate that the emissions of cold start are much higher than that of the hot start. The conversion efficiency of particular matter (PM) is only 33%, which is 31% lower than that of the hot start. Besides, the conversion efficiency of PM is weak under the cold start, and high exhaust flow, and the phenomenon of blow-off is prone to happen. The conversion efficiencies of NOx, HC, and CO are 86%, 79% and 63%, respectively, which differs from the hot-start conversion efficiency by 10%–16%. And their differences are mainly reflected in the early stage (0–600 s). Overall, the exhaust temperature and flow are important factors that affect the conversion efficiency of the after-treatment system, and the specific process was discussed in this paper. These provide enlightenment/direction for the emission reduction of non-road diesel engines.

Short-sea shipping contributions to particle concentration in coastal areas: Impact and mitigation

• Short-sea shipping visibly contributes to particles concentrations in coastal areas. • The bottom-up model predicts consistent particle number concentration, PN, values. • Differently, contribution of ships on PM2.5 cannot be inferred by bottom-up model. • Existing regional fuel quality restrictions mostly reduce PM2.5 emissions. • Cleaner fuels and available after-treatment systems highly reduce PN/PM2.5 levels. Several studies indicate that short-sea shipping is an important source of air pollution for coastal areas and port cities. This paper reports results of a non-reactive particles dispersion model and a new set of experiments implemented for the Channel of Procida (Italy), an area with a high signal-to-noise ratio, due to intense marine traffic and low background pollution. The model successfully predicts particle number concentrations but underestimates PM 2.5 data. Model and experiments show that thanks to the EU policies on marine fuels, the Channel of Procida already has good air quality levels. Besides, the paper demonstrates that fostering the use of LNG or methanol or the application of an exhaust-gas-cleaning-system may allow reducing particles emissions well above 90%. The reliability of control strategies and the benefits for the population suggest that the introduction of regulations on particles emissions for ships can be a realistic option for the future environmental policy agenda.

Effects of Catalyst Structural Parameters on the Performance of Exhaust Gas Aftertreatment System of Diesel Engines

Effects of Catalyst Structural Parameters on the Performance of Exhaust Gas Aftertreatment System of Diesel Engines

Investigation of real operation gaseous emissions from a diesel locomotive

• The high BSFC at the idle operation decreases as the BMEP increases. • Highest BTE at the mid-BMEP, corresponding to 50% load condition. • Total amount of gaseous emissions increases as the BMEP increases. • Lowest brake specific gaseous emissions at the mid-BMEP. • Test mode including high emission-measured condition provides with low uncertainty. Many investigations on the fuel consumption and the emission characteristics of diesel engines for non-road mobile machinery (NRMM) have been carried out in the various conditions of steady-state and transient operation, and the knowledge obtained from these studies provides substantial information to analyze real operation emissions. Detailed information on the fuel efficiency and the emission under the real operation condition, however, is still needed to provide significant information to develop the advanced after-treatment system as well as to analyse the fuel efficiency and emissions from the NRMM operating real-world conditions. This study aims to investigate the fuel efficiency and the gaseous emissions from a diesel locomotive. The experiment was carried out with a Portable Emissions Measurement System (PEMS), and studies the fuel efficiency, the overall gaseous emissions, the association of gaseous emissions and brake mean effective pressure (BMEP), and the load conditions for the emission measurement.

Design and Analysis of Cost reduced Diesel Exhaust Aftertreatment system against Flex Module

Abstract : This research paper represents Designing of Cost reduced Diesel Exhaust Aftertreatment system against existing Flex Module aftertreatment system. Methods represents the steps to design new cost reduced Aftertreatment system. Study involves how new design is still meeting existing space claim and meeting all performance requirements. Simsolid software were used to calculated Modal and Static structural analysis to compare both the designs & ARAI test facility has been used to validate new deign meets Emission compliance as per BS6 Limit for MHCV Norms.

Fast Diesel Aftertreatment Heat-Up Using CDA and an Electrical Heater Between 1.2 and 5.0 kW

Commercial vehicles require fast aftertreatment heat-up in order to move the selective catalytic reduction catalyst into the most efficient temperature range to meet upcoming NOX regulations while minimizing CO2. This study is a follow-up study using an electric heater upstream of a LO-SCR followed by a primary aftertreatment system having an engine equipped with cylinder deactivation. The focus of this study is to minimize the maximum power input to the e-heater without compromising tailpipe NOX and CO2. A system solution is demonstrated using a heavy-duty diesel engine with an end-of-life aged aftertreatment system targeted for 2027 emission levels using various levels of controls. The baseline layer of controls includes cylinder deactivation to raise the exhaust temperature more than 100°C in combination with elevated idle speed to increase the exhaust mass flow rate through the aftertreatment system. The engine load is adjusted to compensate for generating electrical power on the engine. The combination of electrical heat, added load, cylinder deactivation, and elevated idle speed allows the aftertreatment system to heat up in a small fraction of the time required by today’s systems. This work was quantified over the cold federal test procedure, hot FTP, low load cycle (LLC), and the U.S. beverage cycle showing improved NOX and CO2 emissions. The improvement in NOX reduction and the CO2 savings over these cycles are highlighted.