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Technical Paper

LOTUS: A Co-operation for Low Temperature Urea-Based Selective Catalytic Reduction of NOx

The European research co-operation Lotus is presented. The main objectives of the project were i) to show the potential for a urea-based SCR system to comply with the EU standard of years 2005 and 2008 for heavy-duty Diesel engines for different driving conditions with optimal fuel consumption, ii) to reach 95 % conversion of NOx at steady state at full load on a Euro III engine, iii) to reach 75 % NOx reduction for exhaust temperatures between 200-300°C, and 85 % average NOx reduction between 200-500°C. The energy content of the consumed urea should not exceed 1.0 %, calculated as specific fuel consumption. These targets were met in May 2003 and the Lotus SCR system fulfilled the Euro V NOx legislative objectives for year 2008.
Technical Paper

Modeling an Ammonia SCR DeNOx Catalyst: Model Development and Validation

A 1-D numerical model describing the ammonia selective catalytic reduction (SCR) de-NOx process has been developed based on data measured on a laboratory microreactor for a vanadia-titania washcoated catalyst system. Kinetics for various NH3-NOx reactions were investigated, as well as those for ammonia, CO and hydrocarbon oxidation. The model has been successfully validated against engine bench measurements, over light-off and ESC tests, under a wide range of conditions, e.g. flow rate, temperature, NO2/NO ratio, and ammonia injection rate. A very good agreement between the experimental data and the model has been achieved. The model has now been used to predict the effect of NO2/NO ratio on NOx conversion, and the effect of different ammonia injection rates on the efficiency of the SCR process.
Technical Paper

Vehicle Study on the Impact of Diesel Fuel Sulfur Content on the Performance of DeNOX Catalysts and the Influence of DeNOX Catalysts on Particle Size and Number

A vehicle investigation programme was initiated to evaluate the influence of diesel fuel sulfur content on the performance of a DeNOx catalyst for NOx control. The programme was conducted with a passive DeNOx catalyst, selected for its good NOx reduction performance and two specially prepared fuels with different sulfur contents. Regulated emissions were measured and analysed during the course of the programme. The NOx conversion efficiency of the DeNOx catalyst increased from 14 to 26% over the new European test cycle when the sulfur content of the diesel fuel was reduced from 49 to 6 wt.-ppm. In addition the number and size of particles produced using 6 wt.-ppm sulfur fuel were measured by two different techniques: mobility diameter by SMPS and aerodynamic diameter by impactor. The influence of the assumed density of the particulate on the apparent diameters measured by the two techniques is discussed.
Technical Paper

Influence on Particles in Diluted Diesel Engine Exhaust Gas

This paper presents the results of experimental and theoretical investigations on measuring particulate emissions of diesel engines in a dilution tunnel. The results offer a contribution to understanding the influence of several parameters on the particle phase of exhaust gas when diluted and mixed with air. These parameters include the exhaust gas temperature, the dilution ratio of the exhaust gas in the air, the mixture temperature, the flow and mixture conditions, the amount of filter loading and the filter material. In order to determine which physical/chemical processes dominate particle formation in diluted exhaust gas, the results of calculations in terms of condensation and adsorption are compared with the experimental findings. An increase in measured particulate concentrations is generally favoured by short sampling times, fast mixing processes, high exhaust gas temperatures, low mixture temperatures and low dilution ratios.
Technical Paper

Impact of Particulate Traps on the Hydrocarbon Fraction of Diesel Particles

Particulate traps reduce particle emissions through the physical filtration of solid, predominantly carbonaceous particles and decreasing particle-bound hydrocarbon emissions. Catalyst coated and uncoated traps were examined for their ability to reduce particle-bound hydrocarbons. At low exhaust temperatures some volatile hydrocarbons are particle-bound in the trap and are physically retained. These components become gaseous and are purged from the trap with sharp exhaust temperature rises. Oxidation catalysts considerably improve the ability of traps to decrease particle-bound hydrocarbon emissions, particularly PAH at low exhaust temperatures. Precious metal coated traps generate sulfate particles so that especially at high exhaust temperatures the overall filter efficiency can be reduced.
Technical Paper

Modular Trap and Regeneration System for Buses, Trucks and Other Applications

A modular particulate trap system for buses, trucks and other applications consiting of honeycomb traps and an electrical regeneration system has been designed and tested on a test bench and in a city bus. For regeneration, the soot is ignited at the entrance of the trap channel by electric heaters. After ignition, the soot burns self-supporting without further energy supply. Regeneration is possible over the whole engine map. The electrical energy consumption of the heaters for a city bus is in average below 100 W. The filtration efficiency of the system including regeneration is about 80 % during transient city driving. During regeneration, appr. 98 % of the accumulated hydrocarbons adsobed to the soot in the trap are burned off the initiated combustion front. Additionally, the odor of the diesel engine exhaust gas behind the trap is lowered at low engine load even during regeneration.
Technical Paper

Self-Supporting Regeneration of Diesel Particulate Traps

Diesel soot collected in a catalytically coated ceramic honeycomb trap, burns self-supporting, if the heat loss is less than the heat release due to soot oxidation. Experimental verification has been accomplished using a 4.66″ × 6″, 100 CPI trap. Ignition time and regeneration time are measured. At low speeds, a minimum ignition time of 15 s would be sufficient for the trap regeneration. An extended channel with an observation window is provided to allow examination of the regeneration. The soot is ignited at the beginning of the channel and the flame propagation is then observed. The soot burns through the channel in a match-like manner. Manganese and iron fuel additives are observed to have an effect on the mechanism of flame propagation.
Technical Paper

Possibilities of Particle Reduction for Diesel Engines

Particulate emissions from diesel engines mainly consist of soot and high-boiling hydrocarbons (volatile fraction). To reduce the volatile fraction different precious metals and their combinations are tested in traps and supports especially at low loads. A sufficient catalyst's efficiency at low exhaust-gas temperatures (low load) requires a large active catalyst surface. Due to the soot in the diesel exhaust-gas, the catalyst can be covered by a soot layer reducing the catalyst's efficiency. The accumulated soot in the trap must be oxidized. Nonprecious metal catalysts are able to lower the soot ignition temperature. The reduction in ignition temperature depends on the catalyst material used. The influence of the catalyst's concentration and the use of an additional washcoat are also investigated.
Technical Paper

An Exhaust Gas Aftertreatment System to Reduce Particulates for Full-Size Passenger Cars

An exhaust gas aftertreatment system employing thermal regeneration has been developed to lower the particulate emissions from the intercooled Volvo 760 turbo-diesei engine. This system consists, primarily, of a honeycomb trap, a modified exhaust manifold and controlled compressor and intercooler bypasses. With this aftertreatment system, the particulate emissions can be lowered below the 0.2 g/mi standard (FTP-75 cycle) without unacceptable deterioration of the other pollutant emissions and the vehicle driveability. After operating the vehicle for more than 220 miles over consecutive FTP test cycles, the backpressure was found to remain constant up to approximately 70 miles. A brief description of the vehicle test procedure, accomplished during low ambient temperatures, is also provided. Problem areas which still remain are temperature control and thermal resistance as they relate to trap durability.
Technical Paper

Mechanism of the Deposit Formation at Inlet Valves

The deposits on intake valve tulips of spark ignition and diesel engines can produce an increase in fuel consumption and exhaust gas emission, a deterioration of the driving behavior as well as mechanical defects. The formation of these deposits is investigated with respect to different engine parameters and by using a commercially available leaded fuel without additives. The valve deposits are formed by composing and decomposing phenomena which occur in parallel. The composing elements are oil, particles coming from the combustion chamber via the internal exhaust gas recirculation and, partially, fuel components. The deposits are reduced by the liquid fuel coming in contact with the valve tulips and by a high rate of oil flow. To the end of a shorter test duration and less test efforts a short-time simulation to investigate the deposit formation on inlet valves will be described.
Technical Paper

Influences of Future Diesel Fuels on Combustion and Emissions of a Dl-Diesel Engine

Diesel fuels have been tested in both a naturally aspirated and an externally supercharged single cylinder, air cooled KHD DI-diesel engine, to determine the influence of poor fuel quality on combustion and emissions. A thermodynamic analysis of the cylinder pressure was conducted and the emissions were measured both gaseous as well as the particle emission (by means of a dilution tunnel). Additionally, extensive cold start tests were conducted. Under steady state conditions the cetane number seems to be a good parameter which describes the ignition behavior of different fuels. At low load, a change in combustion and a high increase in CO, HC and particle emissions were found with decreasing cetane number. During cold starting and warming up, a clear deterioration of the emission and combustion characteristics was also observed with decreasing cetane number when basic fuels were used.
Technical Paper

Investigation on Particle Size Distribution in the Cylinder of a Passenger Car DI Diesel Engine Using a Fast Gas Sampling Valve

This paper describes research and development activities dealing with a technique which allows the measurement of gaseous and particulate concentrations inside the combustion chamber. This so-called fast-timed gas sampling technique was used for both the observation of the development of gaseous pollutants and soot during combustion and expansion and for getting information about the particle size history. The system has been applied to a modern passenger car DI diesel engine (Volkswagen). The investigation covers the early combustion phase beginning with the start of combustion and throughout the expansion phase until exhaust valve opening. Particles with a size of about 10 nm up to 1 μm were found. Slight variations in the smaller size classes could be observed during the combustion and expansion process.
Technical Paper

Mechanisms of Deposit Formation in Internal Combustion Engines and Heat Exchangers

During the lifetime of an internal combustion engine, deposits are formed at various locations. In diesel engines, deposits in the combustion chamber and at the injection nozzles lead to an increase in the emissions, especially the particulate emissions, and the exhaust gas odor. Additionally, durability problems can also arise. Deposits in the combustion chamber of SI engines can increase the octane requirement, deposits at intake valves can reduce engine efficiency and driveability and increase emissions. A detailed theory on the mechanism of deposit formation, considering the physical effects, is presented. This theory contains a deposit transport mechanism, a mechanism of deposit attachment including an induction phase, a deposit growth phase and a deposit removal mechanism. This complex theory is based on fundamental investigations at different locations in and around internal combustion engines.
Technical Paper

Analysis of the Particle Size Distribution in the Cylinder of a Common Rail DI Diesel Engine During Combustion and Expansion

In the recent years diesel engine developers and manufacturers achieved a great progress in reducing the most important diesel engine pollutants, NOX and particulates. But nevertheless big efforts in diesel engine development are necessary to meet with the more stringent future emission regulations. To improve the knowledge about particle formation and emission an insight in the cylinder is necessary. By using the fast gas sampling technique samples from the cylinder were taken as a function of crank angle and analyzed regarding the soot particle size distribution and the particle mass. The particle size distribution was measured by a conventional SMPS. Under steady state conditions the influence of aromatic and oxygen content in the fuel on in-cylinder particle size distribution and particle mass inside a modern 4V-CR-DI-diesel-engine were determined. After injection and ignition, mainly small soot particles were formed which grow and in the later combustion phase coagulate.