Search Results

1 A methodology for correctly matching trap systems to the vehicle types was developed within the scope of a feasibility study to retrofit the entire Swiss fleet of on-road HDV. Representative test vehicles from 11 vehicle categories were equipped with high capacity data loggers during a period of 4-6 weeks. Statistical evaluation of exhaust temperatures indicate that data on averages, peaks and frequency distributions alone can be misleading, because these tend to over-estimate the available exhaust enthalpy. Analysis of dwell time intervals, at certain temperature levels, is a better method to assess the energy available for the regeneration. Such verification of duty cycles is indispensable before retrofitting traps and choosing either active or passive regeneration systems.

Swiss EPA and European occupational health authorities have sponsored the development of a new sampling and measuring system designed to fulfil future requirements of differentiated particle analysis in field use and for certification purposes. The system suppresses the formation of condensates by applying hot dilution. Solid carbonaceous particles are distinguished from ash particles by means of two different sensors. Particles are size classified by their mobility; their active surface is measured. The measurable size ranges from less than 10 nm to 1 micrometer. The detection limit corresponds to a mass concentration of elemental carbon (EC) of about 0.1 μg/m3. The time resolution of 1 second is suitable for on-line analysis of particulate emission during all types of transient cycles, even no-load acceleration. The system includes a compact diluter with tunable dilution factor from 30 to 3000.

In an attempt to improve ambient air quality, retrofit programmes have been encouraged; targeting reductions in PM emissions by means of diesel particulate filters (DPFs). However depending on the DPF design and operating conditions increased nitrogen dioxide (NO2) emissions have been observed, which is causing concern. Previous work showed that retrofitting a DPF system employing a fuel borne catalyst (FBC) to facilitate regeneration, reduced NO2 emissions. This paper outlines the investigation of a base metal coated DPF to enhance the reduction of NO2. Such a DPF system has been fitted to older technology buses and has demonstrated reliable field performance.

For many years now, epidemiologists have been highlighting the potential damage to health and the associated cost, caused by diesel particulate emissions. There is still debate concerning the crucial characteristics of these particles, however many authorities have concluded that it is their duty to legislate the reduction of such emissions. The most common approach is to legislate that all new vehicles should meet ever stricter emissions limits. This puts the onus and the cost on the engine manufacturers. The emissions limits in developing countries are inevitably less stringent than those in the developed world, this gives the indigenous manufacturers the opportunity to compete and develop. However, vehicle replacement intervals dictate that the effect of legislation controlling new vehicles takes many years to propagate throughout the existent vehicle fleet.

Particulate traps are mechanical devices for trapping soot, ash and mineral particles, to curtail emissions from Diesel engines. The filtration effectiveness of traps can be defined, independent of the pertinent engine, as a function of the particle size, space velocity and operating temperature. This method of assessment lowers cost of certifying traps for large-scale retrofitting projects [1,2]. VERT [3] is a joint project of several European environmental and occupational health agencies. The project established a trap-verification protocol that adapts industrial filtration standards [4] to include the influence of soot burden and trap regeneration phenomena. Moreover, it verifies possible catalytic effects from coating substrates and deposited catalytic active material from engine wear or fuel/ lubricant additives.

Forthcoming emissions legislation is driving the passenger car manufacturers towards the fitting of Diesel Particulate Filters (DPFs) as original equipment. In areas with a particular problem such as heavily congested city centres, retrospective legislation has also been introduced, for example in Hong Kong and Tokyo. Legislation mandating the retrofitting of DPFs obviously has an immediate effect on particulate emissions. Other authorities are thus investigating the efficacy of such measures. However with the increasing use of DPF technology concerns are now being raised over some currently unregulated emissions such as ultra fine particulate and NO2, although total particulate mass and oxides of nitrogen are regulated. To add to the data base for such issues a programme of work was run using London Black Cabs. Four cars were fitted with a DPF, an on-board dosing system to meter a fuel borne catalyst (FBC) into the fuel and a data logger to monitor the DPF performance.

Forthcoming emissions legislation is driving the passenger car manufacturers towards the fitting of Diesel Particulate Filters (DPFs) as original equipment. However such initiatives are not retrospective and due to the replacement rate of the vehicle fleet, there is a time lag before the full benefit of the new measures are fully realised. To overcome this drawback, in areas with a particular problem such as heavily congested city centres, retrospective legislation has been introduced, for example in Hong Kong and Tokyo. Legislation mandating the retrofitting of DPFs obviously has an immediate effect on particulate emissions. Other authorities are thus investigating the efficacy of such measures. To add to the data base for such assessments Octel is running a demonstration programme using London Black Cabs. Four cars have been fitted with a DPF, an on-board dosing system to meter a fuel borne catalyst (FBC) into the fuel and a data logger to monitor the DPF performance.

Growing concern over the health effects of airborne particles and a desire to reduce the associated cost has resulted in legislation, regulations and other measures, in the industrialised world to severely restrict particulate emissions from diesel-fuelled automotive transport. Developing countries are also introducing initiatives to try and reduce emissions, an example is the legislation in India to replace diesel engines with gas fuelled engines in some major conurbations. Such measures are expensive, both in terms of replacing the engines of the vehicles and of implementing the required infrastructure. There is still also debate over whether such measures reduce the number of ultra-fine particulates. A well-proven alternative is to fit diesel engines with Diesel Particulate Filters (DPFs), either as original equipment or as a retrofit system. Regenerating DPFs has in the past been an obstacle to their widespread application.

A diesel particulate filter (DPF) is a crucial weapon in the fight to control the downsides traditionally associated with diesel engined vehicles. The DPF not only produces the benefits required from an environmental standpoint but also has the consumer benefit of eliminating the visible black smoke associated with diesel engines. Thus DPFs have now become a reality, both for series production vehicles and as a retrofit application. Inevitably there are a number of alternative types of DPF and alternative techniques are used for ensuring they continue to function in an acceptable manner. Due to the complexity of the diesel combustion process and the emissions produced it is only to be expected that a device intended primarily to control one parameter would have some effect on other parameters. This paper looks at some different DPF technologies and how they effect emissions, with the emphasis on particulate emissions and the speciation of oxides of nitrogen.

A novel dosing system for fuel borne catalyst (FBC), used to assist regeneration with a diesel particulate filter (DPF), has been developed. The system was designed for on-board vehicle use to overcome problems encountered with batch dosing systems. Important design features were simplicity, to minimise system cost, and the use of in-line dosing rather than batch dosing linked to tank refuelling. The paper describes the development of the dosing system which continuously doses FBC into the fuel line feeding the engine injection pump. The theoretical considerations behind the concept are explored, together with the realities imposed by fuelling regimes in which a variable proportion of the fuel flowing through the injection pump is passed back to the fuel tank. Two types of system are considered, ie where 1) FBC is added to the fuel in direct proportion to the flow rate of fuel and 2) FBC is added at a constant time-based rate.

By means of catalysts, either coatings or fuel-borne, the temperature level for triggering the combustion of soot stored in particulate traps can be lowered from 600°C to 300°C, in case of CRT even to 250°C; but even that may fail, if in dense traffic application of a city-bus only 150 - 200°C are attained - similar situations of low load duty cycles exist in most other applications too. Mere passive regeneration may then not be sufficient, active support is needed. This paper presents an “active” method applicable to any Diesel engine to increase the exhaust temperature whenever required: load of Diesel engines is controlled by the fuel flow only; consequently, excess of air above stochiometric requirement is increasing from λ = 1.5 to λ = 8 with decreasing load, which is in fact the principal cause of the low temperature at light loads.

Future emissions limits are pushing vehicle manufacturers towards the fitting of Diesel Particulate Filters (DPFs) as original equipment. However due to the replacement rate of the vehicle fleet, there is a delay before the full benefit of these measures are fully realised. To overcome this problem, in areas with a particular problem such as heavily congested city centres, retrospective legislation has been, and may be introduced. Legislation mandating the retrofitting of DPFs obviously has an immediate effect on particulate emissions. In some countries including the UK there are also fiscal incentives to fit DPFs. Due to its duty cycle the London taxi or Black Cab is one of the more challenging areas of application for the DPF. Previous work has shown that the use of a fuel borne catalyst (FBC) can extend the operating range of DPF systems providing the possibility of a viable system for such applications.

Ceramic fibers with high specific surface area and adequate high-temperature strength are commercially available for filtration of diesel particulates and in-situ hot regeneration. The manufacturing of a deep bed filtration medium, using such brittle fibers, became possible after a special knitting technique was developed which forms the loops with minimum friction and pretension. Within this structure, the fibers are very little constrained and expose their active surface almost completely. Hence, high filtration efficiencies in the range of 95% could be demonstrated with favorable back-pressure characteristics. Blow-off phenomena were never observed. Endurance testing on engines, with full-flow burner regeneration, proved the high robustness to mechanical and thermo-mechanical loading. This is one of the particular advantages of the new concept.

Pure rape seed oil (RSO), as coded BO100 (BO: Bio-Oil) to distinguish from biodiesel was investigated for a range of intake oxygen levels from 21 to 24%. RSO can have deposit problems in both the fuel injector and piston crown and elevated intake oxygen levels potentially could control these by promoting their oxidation. Increased intake oxygen elevates the peak temperature and this promotes the oxidation of soot and volatile organic compounds. The effect of this on particle mass and on the particle size distribution was investigated using a 6-cylinder 6-liter Perkins Phaser Euro 2 DI diesel engine. The tests were conducted at 47 kW brake power output at 1500 rpm. The particle size distribution was determined from the engine-out exhaust sample using a Dekati microdilution system and nano-SMPS analyzer. The results showed that for air RSO had higher particle mass than diesel and that this mass decreased as the oxygen level was increased.

A dosing system has been developed to facilitate the addition of a fuel borne catalyst (FBC) to a vehicle's fuel supply. The on-board dosing system was primarily designed to reduce cost and complexity. One embodiment of the design provided an additional benefit, namely the automatic adjustment of treat rate according to duty cycle. For high duty operating cycles where average exhaust gas temperatures are high, a low treat rate of FBC is supplied. Conversely at low duty where the exhaust temperature is lower, a higher treat of FBC is delivered. Data from field applications are presented to demonstrate this feature.

Fine pored hot gas traps have filtration efficiencies exceeding 99% of the solid particles in the diesel exhaust gas. There is a favorable trend to deploy this technology ex-factory and retrofitting on-road and off-road engines. The trap system however functions as a chemical reactor. The filter has a large effective area and the engine exhaust gas has plenty of reactants, which can promote undesirable chemical reactions that release toxic secondary emissions. These effects may be amplified when traps have catalytic influence, e.g. due to surface coatings or fuel-borne catalysts. The VERT suitability tests for particle trap systems therefore include a detailed test procedure for verifying the presence of over 200 toxic substances. These include PAH, nitro-PAH, chlorinated dioxins, furans as well as metals. The paper describes test procedures, test reporting, sample extraction and analysis.

Metallic substances, usually added to fuel as organic compounds are, as fuel additives proven to curtail particulate emissions from diesel engines and, as fuel borne catalysts (FBC), to promote regeneration of particle traps. During combustion, these substances form catalytic metal oxides and exit the combustion chamber as ultra-fine solid clusters in the mobility diameter range of 5-30 nm. Particles of this size and composition have a health impact and should not enter the respiratory air. FBC should therefore only be used together with particle traps, which can efficiently collect these metal oxide particles at all operating conditions. This and other requirements are stipulated in the VERT suitability tests for particle trap systems. The approval procedure includes a particle size-specific analysis to verify trap penetration in trace quantities.

The atomisation characteristics of DI diesel engine fuel injection nozzles have been the subject of intensive study over the last decade. Much of this work has been related to clean, single hole nozzles spraying into quiescent air, at either ambient conditions or elevated pressures and temperatures. Experience shows that fuel injector nozzles may foul very rapidly in field service, and that this might have a significant effect on the performance of the engine particularly with regard to emissions. The build up of material on the injector nozzle can be controlled by the addition of suitable fuel additives. This paper describes test procedures developed to assess deposit build up and to indicate the efficacy of keep clean additives. The paper then goes on to describe high speed photographic techniques for studying the fuel spray characteristics of clean and fouled injectors in a firing engine.

High levels of particulate emissions from Diesel engines, in tunnel construction sites, force the aftertreatment of exhaust gases with particulate traps. Sub-micron particulates are suspected to be carcinogenic. Hence, the size distribution of particulates was compared for different particulate trap systems. The two extreme types are the ceramic monolith surface filter and the typical deep-bed filter of knitted fiber. These two types have distinctly different properties. The gravimetric evaluation of both systems show comparable efficiencies around 90%. If, instead, the particle count is evaluated: the efficiency of the surface filter drops below 70%, whereas that of the deep-bed filter increases. The spectral analysis of distinct solid particulates shows that the efficiency of the surface filter deteriorates for particles smaller than 100 nm. The toxicological consequences are disquieting.

One of the most promising ways to insure the periodic regeneration of a particulate trap, consists of additising the fuel with organo-metallic compounds. The present paper deals with a novel alkali product, able to promote natural regenerations, for exhaust temperatures as low as 200 °C, and treatment rates as low as 5 ppm metal. Tests have been carried out on a soot reactor and on an engine bench, with various trap locations in the exhaust, showing that the regeneration occurrence depends on temperature, soot mass loaded inside the porous structure and engine conditions. A complete trap cleaning still needs gas temperatures up to 400 °C, which can be encountered for high load conditions of the engine.