Three issues ago (issue number 345), we previously described the diesel fuel supply situation in the UK, the variable quality, how meeting the EN590 diesel specification is no guarantee of trouble-free motoring, and the general picture regarding the use of fuel additives. This follow-up article serves to describe in more detail how fuel additives can help address this variable quality situation in the UK, meet the requirements of modern diesel engines, and how the situation drives a number of key fuel additive solutions.
All of the issues with modern diesel fuels have meant that additive suppliers have had to develop a range of solutions so that the diesel engine under your bonnet still functions as the manufacturer intended. The removal of sulphur from diesel fuel (that would otherwise poison today’s catalyst systems) has reduced the lubricity of the base fuel and can result in premature wear of fuel pumps and injectors. This is countered by using lubricity additives that are compatible with modern engines, oils, and emissions control systems.
A higher biodiesel content – up to seven per cent – in today’s fuels can promote higher water content, which allow bugs to grow in the fuel, hastens corrosion, promotes waxing-up, and other contamination. Combined additives containing demulsifiers, biocides, detergents, and anti-waxing agents prevent such problems. And extreme unseasonal climatic conditions and summer grade fuel that is stored until temperatures drop may challenge the base fuel’s existing anti-waxing properties. Suitable anti-waxing additives are therefore added to the formula to prevent these problems.
The rapidly increasing proportion of imported refined fuel and consequent long transport and storage times present problems for fuels that are increasingly supplied with properties close to the minimum specifications. Again, we have the dangers of high water content, biological growth, corrosion, and of solid deposits forming and being picked up later, all endangering critical fuel injection equipment. These need to be combated with previously mentioned additives, along with effective detergents and chemical stabilisers, like antioxidants.
Added to these challenges, we have increasingly demanding emissions limits, such as those that have been highlighted by recent events. To put the new super-low vehicle emission standards and expectations into context, these limits are now so low that, during regulated tests, the content of some pollutant gases already present in the ambient engine intake air during the tests can itself significantly impact the tailpipe results, and must be accounted for in the final calculations. This regulated reduction in tailpipe emissions has driven vehicle manufacturers to progressively implement changes which have created additional challenges for which fuel additive manufacturers have needed to develop solutions.
Higher fuel injection pressures and operating temperatures that come with higher torque and power outputs, tend to create tenacious varnish or lacquer deposits deep inside injectors in only a few thousand miles, and these latest engines are also less tolerant of water in fuel. So the latest detergent chemistry is therefore required to both prevent and clean up such deposits, with effective demulsifiers to keep water and fuel separate, such that the water is removed in fuel filtration systems.
More sophisticated exhaust after-treatment systems are necessary to meet regulatory requirements and, in adverse conditions – mostly city driving and short trips – blockage of diesel particulate filters (DPFs) and fouling of exhaust gas recirculation (EGR) systems can result. Innovative detergent chemistry can prevent such problems, maintain engine efficiency and, if required, promote diesel particulate filter regeneration.
Complex engine control systems (drive-by-wire, knock sensing, detailed crankshaft speed monitoring etc.) where the engine management system knows the fuel quality being burnt can make further demands. If the fuel quality is poor, the system adjusts automatically to protect the engine, but lowers engine efficiency, and in turn results in poorer fuel economy. If the fuel quality is good, then drivers will usually notice this from the way that the engine responds. Cetane value improvers and effective detergents can ensure that this desirable situation is present for owners.
Suitable fuel additives to meet all these challenges are developed and then added to the fuel – either as part of a branded retail forecourt fuel, or alternatively in the form of after-market additives. The selection of which package of components needs be formulated depends upon the required benefit claims, and therefore marketing strategy of each company. Careful selection of the fuel additive components is required by a manufacturer – not only to ensure that they all perform correctly, but such that they remain stable during storage, way before they even get into the fuel. If not developed correctly, fuel components can either fall out of solution under cold conditions, or react with one another when heated up.