Diesel Oxidation Catalyst Performance Research Articles

Investigation of the impacts of regeneration temperature and methanol substitution rate on the active regeneration of diesel particulate filter in a diesel-methanol dual-fuel engine

Methanol (CH3OH), a sustainable fuel derived from many renewable resources, simultaneously reduces nitrogen oxides (NOx) and particulate matter (PM) in diesel-methanol dual-fuel engines. This study systematically investigated the effects of regeneration temperature and methanol substitution rate (MSR) on the performance of diesel oxidation catalyst (DOC), diesel particulate filter (DPF), and the temperature characteristics of DPF substrate during active regeneration. The experimental results show that the DOC catalytic oxidation of unburned CH3OH has a conversion rate of more than 97.5 % across various MSR. DPF inlet temperature rose faster with higher MSR. Elevated regeneration temperature reduced effective regeneration times and diesel equivalent consumption. Within active regeneration conditions with MSR increases, both effective regeneration times and diesel equivalent consumption initially decreased and then increased as the MSR rose. At MSR = 30 %, the duration of effective regeneration times during DPF active regeneration was minimized, and diesel equivalent consumption at MSR = 30 % experienced an improvement of 22.52 % compared to MSR = 0 %. The highest DPF substrate temperatures across various MSR levels are consistently observed at T6 position within the DPF. This study can provide a theoretical basis for the active regeneration of DPF in methanol-diesel dual-fuel mode.

State of the art developments in oxidation performance and deactivation of diesel oxidation catalyst (DOC)

State-of-the-art developments in oxidation activity and deactivation mechanisms of the diesel oxidation catalyst (DOC) are reviewed. The effect of temperature, hydrocarbons, CO, H2O, hydrogen, NO, oxygen, NO2, precious metals, and catalyst zoning on DOC's performance is analyzed. CO, NO, and hydrocarbon oxidation is self-inhibited. Hydrogen reduces the light-off temperatures of CO and hydrocarbons. Oxygen and NO2 act as oxidants. Hydrothermal, sulfur, chemical, and hydrocarbon poisoning are primary deactivation mechanisms. Hydrothermal deactivation is the leading cause of Pt-catalyst, and others are less severe. Further improvements regarding biodiesel impact, phosphorous poisoning, and hydrothermal stability are needed to advance DOC science.

Understanding the impact of poison distribution on the performance of Diesel oxidation catalysts

Detailed understanding of the poisoning mechanism in Diesel oxidation catalysts (DOCs) is the key to prevent long term catalyst deterioration in vehicles. The present work studies artificial phosphorus (P) poisoning methods applied to a commercial DOC. Cores of the DOC monolith were exposed to increasing amounts of P precursor by impregnation and by spraying. While impregnation leads to a homogeneous poison distribution in the catalytic layers, elemental analysis revealed that the spraying results in radial and axial P gradients that mimic the distribution of this poison previously observed in vehicle aged DOCs. The activity tests under simulated Diesel exhaust evidenced that P deposition by spraying was more detrimental than by impregnation and caused a more severe decrease in NO oxidation performance. Sequential treatments comprising exposure to P, thermal treatment and exposure to sulphur (S) interleaved by activity tests were performed to gain deeper insight into the catalyst deactivation mechanism.

Pollutant emissions and diesel oxidation catalyst performance at low ambient temperatures in transient load conditions

In this paper an experimental analysis of the ambient temperature effect on diesel engine pollutant emissions is carried out. The study is focused on hydrocarbons and carbon monoxide of both engine out pollutants formation analysis and diesel oxidation catalyzer (DOC) performance. The experiments were carried out at transient engine load conditions of Worldwide harmonized Light vehicles Test Cycle (WLTC) at two levels of ambient temperature: 20 °C and −7 °C. The study presented in this work shows significant different results depending on the pollutant analysed. Regarding hydrocarbons, a significant dependence of pollutant formation on ambient temperature is observed, being the emissions at −7 °C between two and three times the emissions at 20 °C. The DOC performance between temperatures shows similar conversion efficiency. In the case of carbon monoxide formation, temperature dependence plays a less important role than the engine load conditions. The reduction of air fuel ratio at transient conditions drives to unsteady CO profiles emissions along the WLTC that reduce the pollutant conversion with a greater negative impact at −7 °C.

Biofuel blend late post-injection effects on oil dilution and diesel oxidation catalyst performance

In this article, the effects of different biofuel–diesel blends on engine oil dilution and diesel oxidation catalyst performance during late post-injections were investigated. The engine tests were made with an off-road diesel engine under low load conditions at 1200 r/min engine speed. During the experiments, oil samples were periodically taken from the engine oil and later analyzed. Emissions and temperatures before and after the diesel oxidation catalyst were also measured. The fuels studied were fossil EN590:2013 diesel fuel, 30 vol.% biodiesel (fatty acid methyl ester) and 30 vol.% hydrotreated vegetable oil, which is a paraffinic diesel fuel fulfilling the EN15940 specification. The novelty of the study is based on two parts. First, similar late post-injection tests were run with blends of both hydrotreated vegetable oil and fatty acid methyl ester, giving a rare comparison with the fuels. Second, oil dilution and the fuel exit rates during normal mode without the late post-injections were measured. The results showed the oil dilution and the diesel oxidation catalyst performance to be very similar with regular diesel and hydrotreated vegetable oil blend. With the fatty acid methyl ester blend, increased oil dilution, smaller temperature rise in the diesel oxidation catalyst and higher emissions were measured. This indicates that during diesel particulate filter regeneration by late post-injections, fatty acid methyl ester blends increase fuel consumption and require shorter oil change intervals, while hydrotreated vegetable oil blends require no parameter changes.

A Parametric Study of Diesel Oxidation Catalyst Performance on CO Reduction in Diesel Dual Fuel Engine Exhaust

In this research study, a synthetic exhaust gas system is employed to simulate various exhaust conditions similar to those from conventional diesel and Dual Fuel-Premixed Charge Compression Ignition (DF-PCCI) combustion. OEM DOC is tested to compare the effectiveness of reducing CO from both exhaust characteristics. Variations of the temperature and the concentration of CO, THC, and O2 are done to investigate DOC performance on CO reductions according to Design of Experiment (DOE) concept. The results showed that in DF-PCCI exhaust conditions, DOC requires higher exhaust gas temperature as well as O2 concentration to reduce CO emissions.

Investigation and analysis into the impact of rapeseed methyl ester biodiesel on the diesel oxidation catalyst performance

The term ‘biodiesel’ refers, in this paper, to the fatty acid alkyl esters derived from vegetable, animal or waste oil feedstocks. Numerous economic and environmental drivers, such as the need for fuel security, the requirement to reduce global carbon dioxide emissions and the volatile price of crude oil, are leading to the production of alternative transport fuels such as biodiesel, and their consumption, in increasing quantities. Most published research has focused on the impact of biodiesel on the engine performance and the emissions and, to a lesser degree, on the intention of understanding the impact on after-treatment systems. Where the after-treatment systems have been considered, studies have mainly concentrated on diesel particulate filters and nitrogen oxide reduction systems. To date, no detailed studies in the open literature have addressed the performance of the diesel oxidation catalyst and, subsequently, this work presents the first thorough examination in this area. This study investigated the relative impacts of thermal and chemical factors, when using rapeseed-based biodiesel, on the performance of a diesel oxidation catalyst. The oxidation reaction intensity inside the catalyst brick was examined and used to identify any possible effects caused by different hydrocarbon speciation when using biodiesel compared with that when using baseline diesel fuel. It was found that the carbon monoxide catalyst conversion efficiency over a legislative driving cycle decreased as the biodiesel percentage increased, with conversion reduced by 10% and 16% for 25% biodiesel fuel blend and 50% biodiesel fuel blend respectively compared with baseline diesel. The reduction in the spatial and temporal average catalyst brick temperature between baseline diesel and 50% biodiesel fuel blend over the New European Drive Cycle was found to be up to 15.5 °C. Catalyst light-off curves showed very similar responses when the engine-out emissions of carbon monoxide and hydrocarbons were closely matched to those of baseline diesel fuel. No statistically significant difference between the light-off temperatures of 50% biodiesel fuel blend and baseline diesel was found, indicating that exhaust gas hydrocarbon speciation did not have a significant impact on the catalyst performance. The results show that the exhaust gas temperature and the energy released during the exothermic reactions within the catalyst are the most significant causes of the variations in the catalyst performance when using biodiesel blends. These findings indicate that the increased use of biodiesel could require after-treatment design and control optimisation to negate an adverse impact on the catalyst light-off time and the catalyst performance.