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Current developments in fuels and emissions regulations are resulting in an increasingly severe operating environment for diesel fuel injection systems. The formation of deposits within the holes or on the outside of the injector nozzle can affect the overall system performance. The rate of deposit formation is affected by a number of parameters, including operating conditions and fuel composition. For the work reported here an accelerated test procedure was developed to evaluate the relative importance of some of these parameters in a high pressure common rail fuel injection system. The resulting methodology produced measurable deposits in a custom-made injector nozzle on a single-cylinder engine. The results indicate that fuels containing 30%v/v and 100% Fatty Acid Methyl Ester (FAME) that does not meet EN 14214 produced more deposit than an EN590 petroleum diesel fuel.

Current developments in fuels and emissions regulations are resulting in increasingly severe operating environment for the injection system. Formation of deposits within the holes of the injector nozzle or on the outside of the injector tip may have an adverse effect on overall system performance. This paper provides a critical review of the current understanding of the main factors affecting deposit formation. Two main types of engine test cycles, which attempt to simulate field conditions, are described in the literature. The first type involves cycling between high and low load. The second involves steady state operation at constant speed either at medium or high load. A number of influences on the creation of deposits are identified. This includes fouling through thermal condensation and cracking reactions at nozzle temperatures of around 300°C. Also the design of the injector holes is an influence, because it can influence cavitation.

In view of increasing concern over diesel particulates and tightening legislation to control their emission, much work has been done to develop diesel particulate filters (DPFs) and systems to allow them to work reliably. Although a filter will effectively trap solid particles, any material in the vapour phase, such as unburned hydrocarbons, may pass through the filter and subsequently condense. The use of a catalytic wash coat, either on the DPF itself or on a separate substrate, has been proposed to oxidise these hydrocarbons and thus reduce the total material emitted. The use of fuel borne catalysts to aid the regeneration of trapped material within the DPF is also well documented. Such catalyst will also catalyse the oxidation of any hydrocarbons bound up within the particulate. The oxidation of such hydrocarbon occurs at a lower temperature than that of carbon itself, thus allowing lower temperature regeneration of the DPF.

Impending legislation will make it almost inevitable that heavy-duty trucks will have to be fitted with some form of particulate removal after-treatment device. The challenge is to provide a system that is not only environmentally acceptable and cost effective but also durable enough to meet the demands of the trucking industry. Diesel particulate filters (DPF), in conjunction with fuel borne catalysts to facilitate regeneration, are now a recognised technology for meeting future passenger car emissions limits. Retrofitting of such systems to older technology vehicles, where specific environmental concerns exist, has demonstrated the possibility of applying this technology to the heavy-duty vehicle sector. Most of these retrofit applications tend to be to vehicles with a relatively low duty cycle. Whereas this type of duty cycle poses the greatest challenge to the successful regeneration of the filters it is not necessarily the most arduous test of the durability of the system.

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.

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.

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.

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.

The influence of swirl on performance and emissions was investigated using a single cylinder Hydra research engine fitted with a high pressure electronic unit injector and a variable swirl mechanism. A large amount of emission data was collected together with the cylinder pressure, fuel line pressure and needle lift signals at a wide range of operating conditions. The influence of a fixed swirl ratio on emissions was also investigated on a Ford HSD425 York engine with conventional injection system and a synopsis of the results is discussed. Laser illuminated high speed cinematography was used to study the interaction of swirl with spray and combustion processes. Data is presented on air- fuel mixing, spray trajectories and flame movement at different operating conditions. Data is also presented to highlight the influence of swirl on the heat release rate, cylinder pressure rise and its relation to measured emission levels, particularly NOx and particulates.

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.

In the quest for improved fuel efficiency and reduced CO2 emissions, motor manufacturers are increasingly turning to the High Speed Direct Injection (HSDI) diesel engine for passenger car use. To achieve acceptable levels of noise and emissions at low loads two stage injection is being utilised. Such injection systems are prone to nozzle coking due to the small fuel metering holes, low opening pressures and low fuel flow rates under part load operation. This coking leads to a rapid deterioration of emissions performance. This paper describes work done to investigate conditions leading to this phenomena and the possible mechanisms involved.

Continuing research into the effect of vehicle emissions is driving legislation, which is increasingly being enacted to encourage the retrofitting of emissions control devices. Of particular concern are emissions of diesel particulate matter and nitrogen oxides. More recently the adverse effects of nitrogen dioxide in particular, have been highlighted. A programme of work is underway in Santiago to demonstrate the suitability of retrofitting diesel particulate filters (DPF) to urban buses. This paper presents data, including regulated and unregulated emissions, from a bus fitted with a DPF that relies on a fuel borne catalyst (FBC) to facilitate regeneration of the DPF.

The most cost-effective way to reduce the level of diesel particulate emissions is to retrofit exhaust aftertreatment devices. While diesel oxidation catalysts will reduce the mass of particles emitted, they will not significantly reduce the number of ultrafine particles, that are considered the most harmful to health. Diesel Particulate Filters (DPFs) are therefore considered the most effective retrofit devices. One obstacle to the widespread adoption of DPFs is that many DPF technologies require low sulphur fuel. Using a Fuel Borne Catalyst (FBC) to facilitate regeneration of the DPF allows a sulphur tolerant DPF system to be produced.

Heat release data have been obtained from a 5 in bore direct injection diesel engine operating over a range of conditions including off-design conditions, such as running at low air to fuel ratios, using six-hole injector nozzles in place of the standard three-hole nozzles, and reducing compression ratio and thereby swirl ratio at tdc. The paper shows that when operating with adequate utilized air fuel ratios (A/Fs) the experimental heat release data could be correlated with a single zone combustion model and that changing the number of nozzle holes or compression/swirl ratio had little effect on the correlation after the initial period of heat release. At inadequate A/Fs a modification to the model to allow for partial combustion was introduced. This improved correlation and enabled reasonable heat release prediction in the cycle synthesis program. Examples are given of heat release and cycle pressure diagrams computed using these models.

An 8.5 inch bore two stroke engine has been modified into a photographic test rig in which pictures of the complete combustion chamber could be taken vertically upwards through a perspex crowned piston, using a high speed camera. Tests were carried out using several nozzles of the same total hole area. Two fuelling rates and three different air supply pressures were used. At each test condition thirteen cycles of fired data were recorded on 16 mm high speed colour film. At the same time synchronised transient cylinder pressure and fuel injection data were recorded using an on-line data acquisition system. Correlation of jet development from photographs with heat release deduced from the cylinder pressure diagrams using a standard single zone technique show differences due to changes in the hole configuration and in air supply pressure, with approximately constant fuel injection rates.

The design and application of a high speed, timed, sampling valve for the extraction of gas samples, at a variety of points and times, from the combustion chamber of a medium speed diesel engine is described. The valve was traversed radially into the combustion chamber and combined with rotation of the central fuel injector gave sampling at sixteen points relative to the fuel spray. For any given sample the valve opened and closed at the same time each cycle. Samples were analysed and the levels of carbon monoxide, carbon dioxide and nitric oxide were recorded for the complete combustion process.

There is mounting worldwide concern over the health effects of airborne ultra-fine particles. Of greatest concern are the risks due to the cancer-inducing properties of these particles and the aggravation of existing respiratory diseases by the ultra-fine (i.e. <2.5 micron) fraction. This disquiet has already resulted in legislation, regulations and other measures, either mandated or proposed, in the industrialised world to severely restrict particulate emissions from diesel-fuelled automotive transport. Emissions of particles from both new and existing vehicles have been addressed. With the rapid growth anticipated in some developing countries they to will need to address this problem. This paper outlines some alternative solutions to the problem, ranging from alternative power sources, alternative fuels, alternative engine technologies and after-treatment strategies. It also outlines what is required to implement these different solutions.

Fuel-borne catalysts are now an accepted means of aiding the self-regeneration of diesel particulate filters (DPFs). In the past it has been possible to assess the effect of these fuel additives by investigating the temperature at which the filter reaches a pressure drop equilibrium. Under these temperature conditions, the particulate matter is oxidised at the same rate as it is being deposited and there is thus no change in pressure drop across the filter. This technique adequately demonstrates the oxidation temperature of the carbon in the presence of the catalyst. However, it is now well known that such fuel additives also influence the low temperature oxidation of particulate bound hydrocarbons. This phenomenon is not detected by the filter equilibrium technique.

Trapping diesel particulates is effective in reducing both the number and the mass of fine particulate emissions from diesel engines, but unless the accumulated soot can be burned out or regenerated periodically, the vehicle to which the trap is fitted will cease to function after a relatively short time. A programme of work with soot traps using a low treat rate iron-strontium organo-metallic fuel additive to assist and secure regeneration has been carried out. As part of this programme, an advanced specification diesel engine passenger car equipped with a diesel particulate filter (DPF), was operated on roads in the UK for approximately 18 months, during which time the vehicle covered over 50,000 km After completion of 50,000 km on roads, the vehicle was operated on a chassis dynamometer to increase the distance covered with a DPF more rapidly to a final total of 80,000 km.