Cold Start Emissions Research Articles

Alternative Catalytic Approach for Reduction of Cold-Start Hydrocarbon Emissions

This paper describes an alternative approach to reduction of cold-start hydrocarbon emissions that allows the engine to operate under rich conditions for stable operation, and makes use of that rich condition to reduce overall hydrocarbon emissions. The approach requires only the addition of a small catalyst with particular catalytic properties. No additional hardware is required, and secondary air pumps, hydrocarbon adsorbers, electrically heated catalysts, heat storage devices, etc. can be removed from the vehicle. Reductions of 30–40% in hydrocarbon emissions were realized over the US FTP-75 test, without changes in calibration, when compared to the base catalyst systems.

From Zr-Rich to Ce-Rich: Thermal Stability of OSC Materials on the Whole Range of Composition

Car manufacturers use close coupled three way catalysts to reduce cold start emissions. These close coupled catalysts must show long term durability and thermal stability at temperatures higher than 1000 °C. Thus, during the past 10 years, a significant amount of attention has been paid to the design of CeO2-ZrO2 OSC materials with improved surface area, phase and OSC stability. Solid solutions of Ce/Zr mixed oxides are now commonly available on industrial scale. Recent studies have demonstrated that the introduction of rare earth oxides promoters such as La, Pr, Nd, Y, Sm [ENGELHARD WO patent o2 30546; OMG-DMC2 EP Patent 1 181 970; DAIHATSU EP Patent 1 174 174; DELPHI US Patent 6 387 338; ENGELHARD WO Patent 02 22242] or aluminium oxide [TOYOTA EP Patent 1 172 139; Kanzawa et al. SAE Technical Paper 2003-01- 0811] in the Ce/Zr matrix is a very good way to improve the thermal stability and the redox properties of these materials. Positive interactions between PGM and these ‘promoters’ are also claimed. Nevertheless, not only the composition but the optimization of the manufacturing processes is a key factor to obtain both high thermal stability (expressed as surface area and XRD phase purity) and OSC. To meet the increasingly stringent emission limits, Rhodia has developed a new generation of CeZr based mixed oxides. These materials show phase stability and thermal stability at temperatures higher than 1100 °C in a wide composition range: from Zr-rich to Ce-rich mixed oxides. These characteristics have been obtained with a new manufacturing process which leads to highly porous materials. The controlled morphology at microscopic and macroscopic scale prevents particle sintering under severe ageing conditions. Such materials are preferred PGM supports for cost effective catalysts with low PGM loadings.

The Potential for Use of Gold in Automotive Pollution Control Technologies: A Short Review

Recent studies relevant to the future use of gold catalysts in the automotive industry are summarized. Gold catalysts have been examined for their potential in low temperature activity to combat cold-start emission problems and removal of NO x from leanburn gasoline and diesel engines. The justification for developing gold catalyst technologies is based both on their promising technical performance and the relatively stable price and greater availability of gold compared with the platinum group metals (PGMs). Use of gold catalysts under mild conditions could also produce lower proportions of CO in the hydrogen streams used for automotive fuel cells and they could be used for the selective oxidation of carbon monoxide in these hydrogen streams in order to increase the efficiency of these fuel cells. Technical barriers are indicated which still remain to be overcome before application of gold catalysts is successful in the automotive sphere.

Secondary-air charger for reducing cold-start emissions

Legislation has promoted continuous further development of the emission standards of gasoline engines. At the same time, the automotive industry has made successful efforts to comply with these standards. For a number of years, secondary-air injection into the exhaust system has been used as an effective means of reducing cold-start emissions. Mann+Hummel has now developed a new principle for the injection of secondary air, the so-called secondary-air charger.

Real-world and type-approval emission evolution of passenger cars

The investigation of several passenger car generations with gasoline engines shows that the emissions depend very strongly on the driving cycle. Official type approval cycles allow just very inaccurate predications about their real-world emissions. The measured gasoline vehicles have up to factor 11 higher real-life emissions than in type approval cycles. However, a clear reduction of real-world emissions can be seen over the different investigated generations of gasoline cars. In addition, it can be seen that the cold start emissions depend strongly on ambient temperature levels for all generations of cars and that the cold start accounts for an increasing part of the total pollutant emissions. As an extreme example, the cold start hydrocarbon emissions of Euro-3 cars at -20°C ambient temperature correspond approximately to those of 1,000 km driving with warm engines.

Dependence of Pt Gate Restructuring on the Linearity of SiC Field Effect Transistor Lambda Sensors

The increasing size of the car fleet makes it important to find ways of lowering the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from emissions at cold start, in the case when gasoline is utilized, and high NOx emissions and particulates from diesel engines. The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose. One way of treating the high NOx levels from diesel engines is to introduce ammonia in the exhausts and let it react with the NOx in a special catalytic converter to form nitrogen gas and water, which is called SCR (selective catalytic reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx or ammonia sensor is needed. This thesis presents the efforts made to test the SiC-based field effect sensor device both as a cold start lambda sensor for gasoline engines and as an NH3 sensor for SCR systems in diesel engines. The MISiC (metal insulator silicon carbide) lambda sensor has proven to be both sensitive and selective to lambda, and its properties have been studied in lambda stairs both in gasoline engine exhausts and in the laboratory. There is, however, a small cross-sensitivity to CO. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The metal tends to form islands by time, which decreases the catalytic activity and thereby gives the sensor, which is binary when fresh, a linear behavior. Successful attempts to prevent the restructuring through depositing a protective layer of insulator on top of the metal were made. The influence of increasing the catalytic activity in the measurement cell was also studied. It was concluded that the location of the binary switch point of MISiC lambda sensors could be moved towards the stoichiometric value if the consumption of gases in the measurement cell was increased. The MISiC NH3 sensor for SCR systems has been shown to be highly sensitive to ammonia both in laboratory and diesel engine measurements. The influence of other diesel exhaust gas components, such as NOx, water or N2O has been found to be low. In order to make the ammonia sensor more long-term stable experiments on samples with different types of co-sputtered Pt or Ir/SiO2 gas-sensitive layers were performed. These samples turned out to be sensitive to NH3 even though they were dense and NH3 detection normally requires porous films. The speed of response for both sensor types has been found to be fast enough for closed loop control in each application.

Methane, benzene and alkyl benzene cold start emission data of gasoline-driven passenger cars representing the vehicle technology of the last two decades

The US urban driving cycle (FTP-75) is widely used to estimate both the emissions under hot engine conditions as well as those associated with the cold start. Applying fast analysis techniques such as chemical ionization mass spectrometry (CI-MS) the warm-up behavior of individual vehicles can be monitored at a time resolution of 1 s. CI-MS has been used to investigate the emissions of methane, benzene and the alkyl benzene class of compounds. The amount of the emissions at cold start influence was deduced from the time-resolved emission data of four gasoline-driven vehicle classes representing the vehicle technology of the last two decades. Overall, the emissions of five EURO-0, 20 EURO-1, 18 EURO-2 and so far of six EURO-3 passenger cars were recorded. The test vehicles were selected from the currently operating Swiss car fleet based on the car sales statistics. The average methane, benzene and alkyl benzene cold start emissions are reported using both, the traditional bag method as well as the regression model. At room temperature a clear reduction of 94%, 81% and 85% was found for the methane, benzene and alkyl benzene cold start emissions from EURO-0 to EURO-3 technology, respectively.

The effect of silica:alumina ratio and hydrothermal ageing on the adsorption characteristics of BEA zeolites for cold start emission control

Increasingly stringent legislation has led to the need for better control of vehicle cold start emissions. Research work has identified sodium-BEA zeolite with a silica:alumina ratio of 10 (Na-BEA-silica:alumina=10) as a potential trapping agent for hydrocarbons during vehicle cold start, with desorption occurring only at about the temperature of operation of a vehicle exhaust catalyst.Propene and toluene, used as probe molecules for vehicle emissions, were found to absorb under ambient conditions on all forms of BEA. There appear to be two adsorption mechanisms at play, one involving charge gradients in the zeolite framework and characterised by lower desorption temperatures (molecular adsorption) and the other related to zeolite acidity (oligomeric adsorption).Both the presence of water and simulated ageing reduced the adsorption capacity of the zeolites. Hydrothermal ageing was found to result in dealumination of the zeolite framework, a process that can be reduced by incorporation of lanthanum into the lattice. Water in the gas stream was found to block pores and reduce adsorption. A combination of a more hydrophilic zeolite with BEA zeolite is suggested to overcome the loss in capacity by the presence of water in car exhaust.

A new strategy for improving the warm-up performance of a light-off auto-catalyst for reducing cold-start emissions

Light-off catalysts are often used to minimize cold-start emissions. The improved coldstart performance of light-off catalysts (LOCs) needs the optimal design in terms of flow distribution, geometric surface areas (GSA), precious metal (PM) loading, cell density and space velocity (SV). In this study, these influential factors are numerically investigated using an integrated numerical technique by considering not only the three-dimensional fluid flow but also the heat and mass transfer with chemical reactions. The present results indicate that uneven catalyst loading by depositing highly active catalyst materials upstream of the monolith is beneficial during the warm-up period, but its effect is severely deteriorated when the SV is above 100 000 h-1. To maximize light-off performance, this study suggests that: (a) the LOC be designed as a double-substrate type; (b) a substrate with high GSA and high PM loading at the face be placed at the front; (c) the cell density of the rear monolith be lower to reduce the pressure drop. In this paper, some initial results towards a new strategy of dual substrates are also reported to shorten the light-off time and improve conversion efficiency during warm-up. The proposed approach was very effective in reducing back pressure and cold-start emissions during the early seconds of engine operation.

A practical approach for rapid catalyst light-off by means of strategic engine control

Cold-start emissions pollution from gasoline engines has always been an issue in the urban driving cycle as it contributes a significant share of the overall engine emissions in a typical car journey. Rapid engine warm-up and catalyst light-off are two important factors deciding the overall exhaust emissions in a gasoline-powered electronic fuel injection (EFI) engine. This paper presents a practical approach for rapid catalyst light-off by means of strategic engine control. An existing engine control unit (ECU) was replaced by a programmable engine management system (EMS) so that idling speed, excess-air factor and spark timing can be optimized for improved catalyst light-off at the engine cold-start phase. Results show that with a proper high value of ignition retard (HVIR) control strategy the catalyst light-off time can be shortened to about 40 s with idle speed set at 1750 r/min. Compared with the normal spark timing setting, the cumulative tailpipe emissions during the cold-start phase have been decreased by 90 per cent for CO, 80 per cent for hydrocarbons and 65 per cent for NOx with HVIR implementation. A further increase in the idle speed to 2000 r/min, if allowable, could reduce the catalyst light-off time to less than 30 s from engine cold-start.

Cold-start emissions from petrol and diesel vehicles according to the emissions regulations (from Euro 92 to Euro 2000)

Knowledge of cold-start emissions is one of the major elements in emissions inventories, particularly for urban conditions. Moreover, from January 2000 the new European driving cycle (tests conditions) for vehicle certification (Euro 2000) is modified to properly address this issue (so called deletion of 40 sec.). In order to characterise both the cold driving distance and the relative emissions levels, measurements on a chassis dynamometer with a dilution tunnel have been carried out on 10 vehicles (five petrol cars, five diesel cars - Euro 92, 96 and 2000). Regulated emissions have been measured second by second over cycles based upon repetition of short elementary units derived from the ECE driving cycle in order to reproduce the same kinematics conditions. The stabilisation of the emissions was used to define the end of the cold period. For petrol powered vehicles, the results show that the length of the cold trip is neither dependant on the type of vehicle nor on the cycle. On average, this distance is less than 1.5 km whatever the pollutant you consider. However, better engine management and improvement of the after treatment system allow a significant decrease of the cold-start emissions between 1992 and 2000 technologies. For diesel powered vehicles, cold-start-emissions (cold engine, water temperature below 70°C) are close to hot emissions. Hence, it is not appropriate to talk about cold-start over-emissions for diesel vehicles. The results have shown a great reduction of all the emissions over the urban driving cycle, from 1992 to 2000 technologies.

623 多断層型触媒装置によるコールドスタートエミッションの低減(OS5 21世紀に挑むエンジン技術)

623 多断層型触媒装置によるコールドスタートエミッションの低減(OS5 21世紀に挑むエンジン技術)

A study of HC reduction with hydrocarbon adsorber systems

Hydrocarbon adsorber is considered as a promising technology to reduce cold start HCs in automotive exhaust gas. In this study, three in-line adsorber systems were tried to reduce the cold start emission. To check the basic characteristics of adsorber converters, surface areas, TPD and TPA were examined after a hydrothermal aging. Also idle engine bench was used to find the adsorption and desorption capabilities of the adsorber systems at cold start. Finally a practicability of the adsorber systems for the LEV achievement was checked with FTP test on a 2.0 D M/T vehicle. The results of this study indicate that hydrocarbon adsorber system is one of the promising passive technologies to meet the ULEV regulation.

An urban transport emission model for the Antwerp area

We present a detailed modelling approach which provides hourly emissions of CO, NO x , VOC, PM, SO 2 and Pb for individual streets and road segments in the Antwerp area (20 km×20 km). The hourly emissions are computed as a function of road type, vehicle type, fuel type, traffic volume, vehicle age, trip length distribution and the actual ambient temperature. The traffic volumes are derived from an urban traffic flow model for the city of Antwerp, which contains a network with almost 2000 road segments. The traffic flow model has been implemented in a GIS environment. The emission factors used in the model are derived from the COPERT-II methodology. Cold start emissions and evaporation losses are included in the model. Results are shown for the hourly hot- and cold start emissions obtained for CO, NO x and VOC. For these pollutants a partial validation of the model results was carried out by comparing the COPERT-II emission factors with on-the-road traffic emission measurements carried out for gasoline passenger cars with a closed-loop controlled three-way catalyst.

Uncertainties of modelling emissions from road transport

To determine emission data from road transport, complex methods and models are applied. Emission data are characterized by a huge variety of source types as well as a high resolution of the spatial allocation and temporal variation. So far, the uncertainties of such calculated emission data have been largely unknown. As emission data is used to aid policy decisions, the accuracy of the data should be known. So, in the following, the determination of uncertainties of emission data is described. Using the IER emission model for generating regional or national emission data, the uncertainties of model input data and the total errors on different aggregation levels are exemplarily investigated for the pollutants NO x and NMHC in 1994 for the area of West Germany. The results of statistical error analysis carried out for annual emissions on road sections show variation coefficients (68.3% confidence interval) of 15–25%. In addition, systematic errors of common input data sets have been identified especially affecting emissions on motorway sections. The statistical errors of urban emissions with warm engine on town level amount to 35%. Therefore they are considerably higher than the errors outside towns. Error ranges of additional cold start emissions determined so far have been found in the same order. Additional uncertainties of temporally highly resolved (hourly) emission data depend strongly on the daytime, the weekday and the road category. Variation coefficients have been determined in the range between 10 and 70% for light-duty vehicles and between 15 and 100% for heavy-duty vehicles. All total errors determined here have to be regarded as lower limits of the real total errors.

Thermal stability of metal-supported catalysts for reduction of cold-start emissions in a wood-fired domestic boiler

The aim of the present work is to develop a catalyst based on a mixture of manganese oxides and platinum supported on a metallic monolith for abatement of emissions from wood combustion, particularly during the cold-start phase. The activity and the thermal stability of the catalysts have been studied in the laboratory, before performing tests in a wood-stove. The effect of the hydrothermal treatment at 900°C on the adherence of the washcoat onto a metallic substrate was studied using scanning electronic microscope. It revealed well-adhering washcoat onto the metallic support due to the growth of the alumina whiskers during the treatment. The influence of the amount of washcoat, as well as the influence of the concentration of manganese oxides in it (Mn: 5 to 20 mol%/Al 2O 3) on the activity of fresh and hydrothermally-treated catalysts were studied. The activity tests were carried out using a mixture of carbon monoxide, naphthalene and methane in the presence of air, steam and carbon dioxide to resemble the flue gases from wood combustion. On the fresh catalysts, containing the same total amount of manganese, a high concentration of manganese oxides in the washcoat favoured the oxidation of carbon monoxide and naphthalene, whereas a lower concentration of manganese oxides in the washcoat gave higher activity for the oxidation of methane. An increased total amount of manganese oxides in the catalysts, which had the same amount of washcoat, resulted in an increase in activity for the oxidation of the three combustibles. After thermal treatment at 900°C for 270 h in steam, most of the manganese oxide catalysts were activated for the oxidation of carbon monoxide and naphthalene while only being slightly deactivated for the oxidation of methane. The addition of manganese oxides in the washcoat, however, lowers the temperature of the γ- to α-alumina phase transformation. Platinum (0.5 mol%) was added to the manganese oxide (10 mol%) catalyst to improve its activity. A platinum catalyst was also tested for comparison. The platinum and the mixed catalysts showed similar activity for the oxidation of carbon monoxide and naphthalene, while the mixed catalysts were more active for the oxidation of methane. A similarly mixed MnO x –Pt (10–0.5 mol%) catalyst supported on Al 2O 3 stabilised with 3% lanthanum, but at larger scale, was tested in a wood-stove. The possibility of pre-heating the catalyst during the start-up phase was studied. The tests revealed a strong decrease of the carbon monoxide and unburned hydrocarbons emissions during the start-up phase when the catalyst was pre-heated with hot air compared with no pre-heating or no catalyst.

Cold start emissions at +22, −7 and −20°C ambient temperatures from a three-way catalyst (TWC) car: regulated and unregulated exhaust components

A project initiated by the Swedish Environmental Protection Agency (SEPA) concerning cold start driving conditions is partially reported in the present paper. A three-way catalyst car was run in accordance with the European driving cycle (EDC) at 22°C, −7°C and −20°C ambient temperatures. The diluted exhaust was analyzed for: Carbon monoxide (CO), unburned fuel hydrocarbons (HC), oxides of nitrogen (NO x ), particulates, light aromatics, alkenes, green house gases, aldehydes and polycyclic aromatic hydrocarbons (PAH) in particles and in the gaseous phase. As expected, the emission factors of both regulated and unregulated exhaust components increased at lower ambient temperatures. However, the emissions did not increase uniformly. The mutagenic/carcinogenic compound benz[ a]pyrene for example, increased more than 100 times while CO and HC only increased 5–20 times at the lowest ambient temperature studied.

Use of an Electrically Heated Catalyst to Reduce Cold-Start Emissions in a Bi-Fuel Spark Ignited Engine

Reduction of cold-start emissions using electrically-heated catalyst (EHC) technology was the focus of this work. Comprehensive emission measurements of CO, CO2,NOx, and total hydrocarbons (THC) are reported for a spark-ignited engine operated on baseline gasoline and compressed natural gas (CNG). Electric heating times of 0, 20, and 40 s with and without secondary air injection were investigated. The 40-second electric catalyst heating with secondary air injection scenario yielded the greatest catalyst system (EHC+OEM three-way catalyst) conversion efficiencies for THC, CO, and NOx for gasoline and natural gas fueling. Electric catalyst heating coupled with secondary air injection significantly improved THC and CO emissions for gasoline fueling. THC oxidation was difficult for CNG fueling due to the high content of nonreactive methane in the fuel. The independence of NOx emissions on heating time was demonstrated for all fueling cases.

Thermal Response of Automotive Hydrocarbon Adsorber Systems

Modern hydrocarbon adsorbers for gasoline engines are promising candidates for cold start emission control. In this paper, the flow and heat transfer in a typical complex system, comprising a “barrel type” adsorber and two conventional catalysts is studied. A mathematical model is developed and applied for the computation of the flow and pressure distribution, as well as transient heat transfer in the system. The model is aimed at understanding and quantifying the particular thermal response behavior of hydrocarbon adsorber systems. Illustrative results with variable geometric parameters under realistic input conditions are presented. [S0742-4795(00)01701-4]

Reducing cold-start emission from internal combustion engines by means of a catalytic converter embedded in a phase-change material

Under normal operating conditions, catalytic converters appear to be the most effective means of reducing air pollution from internal combustion (IC) engines. The conversion efficiency, however, declines very steeply for temperatures below about 350°C and is practically zero during the starting and warming-up period. Improving the conversion efficiency under these conditions is important, particularly in large cities, where the number of startings per vehicle per day tends to be high. Among the more successful solutions are preheating of the catalyst electrically, warming up of the catalyst in an external combustion chamber, installation of an auxiliary small-capacity catalytic converter, and employment of an adsorbing unit between two catalysts. Although these methods are quite effective, their disadvantage lies in the fact that they require an external energy source, an additional component (a control unit) or a three-stage catalyst. In the present work an investigation was made of a solution based on the exploitation of thermal capacitance to keep the catalyst temperature high during off-operation periods. A phase-change material (PCM) with a transition temperature of 352.7°C, which is slightly above the light-off temperature of the metallic catalyst, was specially formulated, and a system comprising a catalytic converter embedded in the PCM was designed and tested. Under normal engine operating conditions, some of the thermal energy of the exhaust gases was stored in the PCM. During the time that the vehicle was not in use, the PCM underwent partial solidification, and the latent heat thus produced was exploited to maintain the catalyst temperature within the desired temperature range for maximum conversion efficiency.