Active Diesel Particulate Filter Regeneration Research Articles

Impact of Active Diesel Particulate Filter Regeneration on Carbon Dioxide, Nitrogen Oxides and Particle Number Emissions from Euro 5 and 6 Vehicles under Laboratory Testing and Real-World Driving

Particulate mass concentration is a crucial parameter for characterising air quality. The diesel particulate filter (DPF) is the primary technology used to limit vehicle particle emissions, but it needs periodic cleaning, a process called regeneration. This study aims to assess the impact of active DPF regeneration on the performance and emissions of Euro 5 and 6 vehicles. The study examined both carbon dioxide (CO2) and pollutant (nitrogen oxides (NOx) and particle number (PN)) emissions for eight vehicles tested in the laboratory and on the road. Apart from the DPF, a wide range of emission control systems was covered in this experimental campaign, including exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC), lean NOx trap (LNT) and selective catalytic reduction (SCR) catalyst, revealing the different impacts on NOx emissions. The regeneration frequency and duration were also determined and used to calculate the Ki factor, which accounts for the emissions with and without regeneration, weighted over the distance driven between two consecutive regeneration events. Based on these outcomes, representative emission factors (EF) were proposed for the regeneration phase only and the complete regeneration interval. In addition, the effect of regeneration on efficiency was estimated and compared with other energy consumers. The results indicated a significant impact of DPF regeneration on CO2, NOx and PN emissions, higher in the case of driving cycle testing in the laboratory. The relevant mechanisms behind the elevated emission levels were analysed, focusing on the regeneration period and the test phase following immediately after. The calculation of the Ki factor and the comparison with the official values revealed some weaknesses in its application in real-world conditions; to overcome these, new NOx EF values were calculated, depending on the emission control system. It was revealed that Euro 6 vehicles equipped with SCR could comply with the applicable limits when considering the complete regeneration interval. Finally, it was indicated that the DPF regeneration impact on vehicle efficiency is similar to that of driving with the air conditioning (A/C) system and headlights on.

Study of gas and particulate emission characteristics during the fast regeneration period of DPF

Based on the diesel particulate filter (DPF) regeneration test bench and the particulate loading device, the effects of regeneration temperature and flow rate on the gas and particulate emissions during the fast regeneration period of the DPF are explored. The results show that the fast regeneration period is usually easy to occur during the DPF active regeneration process, which leads to the fast increase of the internal temperature of the DPF substrate. During the fast regeneration process, the gas and particulate emissions in the regeneration process are mainly concentrated in this period, accounting for 45.8%–83.2% and 61%–84% of the total emissions respectively. With the increase of the regeneration temperature, the proportion of gas emissions during the fast regeneration period decreases, while the proportion of particulate emissions remains essentially unchanged. Increasing the regeneration temperature does not significantly improve the regeneration efficiency in the fast regeneration period. With the increase of the flow rate, both the proportion of gas and particulate emissions decrease, and the DPF regeneration is inhabited. On the other hand, after the fast regeneration period, DPF regeneration enters the slow regeneration stage, the economy of input energy for the DPF regeneration gradually decreases. Controlling active DPF regeneration needs to take into account the impact of fast regeneration period on emission and input energy, together with the effect of regeneration temperature and flow rate.

Solid particulate mass and number from ducted fuel injection in an optically accessible diesel engine in skip-fired operation

Ducted fuel injection (DFI) is a novel combustion strategy that has been shown to significantly attenuate soot formation in diesel engines. While previous studies have used optical diagnostics and optical filter smoke number methods to show that DFI reduces in-cylinder soot formation and engine-out soot emissions, respectively, this is the first study to measure solid particle number (PN) emissions in addition to particle mass (PM). Furthermore, this study quantitatively evaluates the use of transient particle instruments for measuring particles from skip-fired operation in an optical single cylinder research engine (SCRE). Engine-out PN was measured using an engine exhaust particle sizer following a catalytic stripper, and PM was measured using a photoacoustic analyzer. The study improves on earlier preliminary emissions studies by clearly showing that DFI reduces overall PM by 76%–79% and PN for particles larger than 23 nm by 77% relative to conventional diesel combustion at a 1200-rpm, 13.3-bar gross indicated mean effective pressure operating condition. The degree of engine-out PM reduction with DFI was similar across both particulate measurement instruments used in the work. Through the use of bimodal distribution fitting, DFI was also shown to reduce the geometric mean diameter of accumulation mode particles by 26%, similar to the effects of increased injection pressure in conventional diesel combustion systems. This work clearly shows the significant solid particulate matter reductions enabled by DFI while also demonstrating that engine-out PN can be accurately measured from an optical SCRE operating in a skip-fired mode. Based on these results, it is believed that DFI has the potential to enable fuel savings when implemented in multi-cylinder engines, both by lowering the required frequency of active diesel particulate filter regeneration, and by reducing the backpressure imposed by exhaust filtration systems.

Active route planning for active diesel particulate filter regeneration

The vehicle route choice has great impact on the vehicle operating conditions, but it has rarely been used as a way to create desired vehicle operation and benefit automotive control. This paper presents a route planning algorithm which generates a route that meets the requirement of high-speed driving time from the diesel particulate filter controller for an active diesel particulate filter regeneration. Real-time traffic information is considered when designing the route. A new routing algorithm based on the unconstrained Dijkstra algorithm is developed to approximately solve this consecutive-highway-time-constrained shortest-path problem. A correctness proof of the algorithm is given based on an augmented graph. Examples are provided to show the scenarios in which the proposed routes can facilitate the diesel particulate filter regeneration control without adding too much travel time cost.

Utilizing low airflow strategies, including cylinder deactivation, to improve fuel efficiency and aftertreatment thermal management

Approximately 30% of the fuel consumed during typical heavy-duty vehicle operation occurs at elevated speeds with low-to-moderate loads below 6.5 bar brake mean effective pressure. The fuel economy and aftertreatment thermal management of the engine at these conditions can be improved using conventional means as well as cylinder deactivation and intake valve closure modulation. Airflow reductions result in higher exhaust gas temperatures, which are beneficial for aftertreatment thermal management, and reduced pumping work, which improves fuel efficiency. Airflow reductions can be achieved through a reduction of displaced cylinder volume by using cylinder deactivation and through reduction of volumetric efficiency by using intake valve closure modulation. This paper shows that, depending on load, cylinder deactivation and intake valve closure modulation can be used to reduce the fuel consumption between 5% and 25%, increase the rate of warm-up of aftertreatment, maintain higher temperatures, or achieve active diesel particulate filter regeneration without requiring dosing of the diesel oxidation catalyst.

Cylinder Pressure Information-Based Postinjection Timing Control for Aftertreatment System Regeneration in a Diesel Engine—Part II: Active Diesel Particulate Filter Regeneration

The successful utilization of a diesel particulate filter (DPF) to reduce particulate matter (PM) in a passenger car diesel engine necessitates a periodic regeneration of the DPF catalyst without deterioration of the drivability and emission control performance. For successful active DPF regeneration, the exhaust gas temperature should be over 500 °C to oxidize the soot loaded in the DPF. Previous research increased the exhaust gas temperature by applying early and late post fuel injection with a look-up table (LUT) based feedforward control implemented into the engine management system (EMS). However, this method requires enormous calibration work to find the optimal timing and quantity of the main, early, and late post fuel injection with less certainty of accurate torque control. To address this issue, we propose a cylinder pressure based multiple fuel injection (MFI) control method for active DPF regeneration. The feedback control of the indicated mean effective pressure (IMEP), lambda, and DPF upstream temperature was applied to precisely control the injection quantity of the main, early, and late post fuel injection. To determine their fuel injection timings, a mass fraction burned 60% after location of the rate of heat release maximum (MFB60aLoROHRmax) was proposed based on the cylinder pressure information. The proposed control method was implemented in an in-house EMS and validated at several engine operating conditions. During the regeneration period, the exhaust gas temperature tracked the desired temperature, and the engine torque fluctuation was minimized with minimal PM and NOx emissions.

Comparison of Parallel and Series Hybrid Power Trains for Transit Bus Applications

The fuel economy and emissions of conventional and hybrid buses equipped with emissions aftertreatment were evaluated via computational simulation for six representative city bus drive cycles. Both series and parallel configurations for the hybrid case were studied. The simulation results indicated that series hybrid buses have the greatest overall advantage in fuel economy. The series and parallel hybrid buses were predicted to produce similar carbon monoxide and hydrocarbon tailpipe emissions but were also predicted to have reduced tailpipe emissions of nitrogen oxides compared with the conventional bus in higher speed cycles. For the New York bus cycle, which has the lowest average speed among the cycles evaluated, the series bus tailpipe emissions were somewhat higher than they were for the conventional bus; the parallel hybrid bus had significantly lower tailpipe emissions. All three bus power trains were found to require periodic active diesel particulate filter regeneration to maintain control of particulate matter. Plug-in operation of series hybrid buses appears to offer significant fuel economy benefits and is easily employed because of the relatively large battery capacity that is typical of the series hybrid configuration.

Impact of Cylinder Deactivation on Active Diesel Particulate Filter Regeneration at Highway Cruise Conditions

Abstract—Heavy-duty over-the-road trucks require periodic active diesel particulate filter regeneration to clean the filter of stored particulate matter. These events require sustained temperatures between 500 and 600□C to complete the regeneration process. Engine operation during typical 65 mile/hour highway cruise conditions (1200 rpm/7.6 bar) results in temperatures of approximately 350□C, and can reach approximately 420□C with late fuel injection. This necessitates hydrocarbon fueling of a diesel oxidation catalyst or burner located upstream of the diesel particulate filter to reach the required regeneration temperatures. These strategies require increased fuel consumption, and the presence of a fuel-dosed oxidation catalyst (or burner) between the engine and particulate filter. This paper experimentally demonstrates that, at the highway cruise condition, deactivation of valve motions and fuel injection for two or three (of six) cylinders can instead be used to reach engine outlet temperatures of 520-570□C, a 170-220□C increase compared to normal operation. This is primarily a result of a reduction in the air-to-fuel ratio realized by reducing the displaced cylinder volume through cylinder deactivation.

Impact of selective catalytic reduction on exhaust particle formation over excess ammonia events.

The introduction of selective catalytic reduction (SCR) aftertreatment to meet stringent diesel NOx emission standards around the world increases exhaust ammonia. Further to the direct air quality and health implications of ammonia, this may also lead to particle formation in the exhaust. In this study, an ammonia SCR system was examined with respect to its impact on both solid and total exhaust particle number and size distribution, downstream of a diesel particulate filter (DPF). Fuel post-injection was conducted in some tests to investigate the effect of ammonia during active DPF regeneration. On average, the post-DPF solid >23 nm and total <23 nm particle number emissions were increased by 129% (range 80-193%) and by 67% (range 26-136%), respectively, when 100 ppm ammonia level was induced downstream of the SCR catalyst. This is a typical level during ammonia overdosing, often practiced for efficient NOx control. Ammonia did not have a significant additional effect on the high particle concentrations measured during DPF regeneration. Based on species availability and formation conditions, sulfate, nitrate, and chloride salts with ammonium are possible sources of the new particles formed. Ammonia-induced particle formation corresponds to an environmental problem which is not adequately addressed by current regulations.

Measuring particulate matter emissions during parked active diesel particulate filter regeneration of heavy-duty diesel trucks

Heavy-duty diesel trucks (HDDTs, >33,000 pounds gross vehicle weight rating) are commonly equipped with diesel particulate filters (DPFs) to meet the California model year (MY) 2007 PM emissions standard. Particulate matter (PM) emissions were measured from nine parked active DPF regenerations of two HDDTs, a 2007 and 2010 MY, using a novel ambient-dilution wind tunnel. This work specifically evaluated PM mass emissions during regeneration by measurements from the following instruments: TSI DustTrak DRX 8533, TSI Engine Exhaust Particle Sizer 3090 (EEPS) and TSI Scanning Mobility Particle Sizer 3936L88 (SMPS), filters by gravimetric analysis, and for one test a Dekati Mass Monitor 230-A (DMM). Active regeneration by fuel injection upstream of the DPF began with the Soot Combustion Regime, where PM emissions had a count median diameter (CMD) of >30nm and some faint gray smoke was observed flowing from the tunnel. During brief moments of the Soot Combustion Regime, the DustTrak DRX reported more than half of the mass was >1µm. As active regeneration continued, aftertreatment inlet temperature increased to >500°C, beginning the Fuel Combustion Regime, defined conversely where the CMD of the emissions was <30nm. Under both regimes, discrepancies were observed between EEPS and SMPS size distributions and improved agreement was attained after performing a post-hoc EEPS correction procedure. The accuracy of the DMM was equivocal; the average DMM emissions rate was within five percent of the gravimetric filter, but the mass distribution was substantially shifted relative to SMPS and EEPS distributions. Uninterrupted parked active regeneration resulted in 13gPM emissions from the 2007 MY and 1.8gPM from the 2010 MY based on filter measurements. The PM mass emissions rates, based on measurements from real-time instruments, show that the contribution of Soot Combustion Regime to total regeneration emissions decreased from 75% to 5% between the 2007 and 2010 MY.

Strategies for active diesel particulate filter regeneration based on late injection and exhaust recirculation with different fuels

Wall flow–type particulate filters are used in diesel vehicle engines to reduce particulate emissions below the limits established in regulations Euro 5 and Euro 6. The soot accumulated in the trap is eliminated during regeneration processes, often combining passive strategies with active ones. Active regeneration is conducted by modifications of the engine control parameters with respect to those set for normal vehicle operation. In this work, three of these parameters were modified to look for an optimized regeneration strategy, considering fuel consumption, gaseous emissions and rate of regeneration. The selected parameters were injection timing (affecting all injection events), exhaust gas recirculation and amount of postinjected fuel. The fuel tested was considered as an additional variable, and therefore, tests were performed with three different fuels: an ultra-low sulfur diesel fuel, a biodiesel fuel produced from animal fat and a gas-to-liquid fuel from low-temperature Fischer–Tropsch process. It...

Analytical investigations on ageing phenomena of catalytic exhaust gas aftertreatment components

Upcoming emission limits for commercial vehicles cannot be maintained solely by modern combustion methods, optimized fuel injection systems and exhaust gas recirculation. In addition, combined exhaust gas aftertreatment systems are necessary. Over engine lifetime, performance deterioration of the exhaust gas aftertreatment systems can be observed. This is influenced by system design as well as operating strategies. The performance deterioration of catalysts is caused by thermal and chemical phenomena. Thermal ageing effects in a combined aftertreatment system containing a diesel particulate filter (DPF) are dominated by the filter active regeneration strategy. Chemical poisoning of the catalysts is caused primarily by engine oil. Content of this study is the analysis of diesel oxidation catalysts from combined aftertreatment systems with varying operation time, but the same total PGM (Platinum Group Metal) loading. The catalysts are investigated regarding deterioration phenomena caused by thermal ageing and chemical poisoning. The catalytic conversion deterioration is correlated with the active DPF regeneration history of the components. As further methods BET, XRF, XRD and FESEM-EDX are applied. A correlation between specific catalyst surface as well as Pt particle size and active DPF regeneration history is investigated. Also, oil consumption and accumulation of poisoning elements on the catalyst surface are analyzed. The determination of clear correlations regarding thermal and chemical ageing phenomena is complicated by the large number of influence factors, as catalysts systems from on-road vehicles with different vehicle weight, operation time, total lube oil consumption and number of active DPF regenerations were analyzed.