Fuel filters on diesel engines and investigation of cold start performance

Diesel engines are now frequently preferred due to their high efficiency and fuel economy. With the development of technology, the fuel systems used in diesel engines also vary. With this review, the injection systems used in diesel engines are investigated. In addition, the system components of the injection systems are reviewed. With the developing of the technology, the fuel injection systems are working with higher pressures and being more sensitive, so that the design of the fuel system is more critical now to be able to operate diesel engines with the fuel economy and higher efficiencies. Due to the increasing sensitivity of the systems, the pollutants (water, particles, air, etc.) in the system and the fuel are more critical to the parts of the system. Therefore, the fuel filters used in the fuel systems have a very important role in terms of having a robust system. In this review, the fuel filters are classified and examined in various aspects, and information about the filtering mechanisms has been given. In particular, problems encountered in cold weather, especially in diesel engines, can be examined to determine what possible failure modes may occur, what root causes this failure modes are and how they can be avoided, the effects of both the environmental and systematic parameters and the effects of these parameters were examined. This investigation consists of 5 main sections. In the first section, the fuel systems used in diesel engines are explained in general. In the second section, all subsystems and parts of the fuel system are introduced. In the third section, the reasons why diesel engines are needed a filtration and how they are made are reviewed in terms of the mechanisms that make up the filter, as well as the pollutants in diesel fuels, the effects of these pollutants on the engine. In addition, filtration and pollution factors in gasoline engines are also mentioned. In the fourth section, factors affecting fuel filter cold working performance are reviewed separately. In particular, the effect of fuel on cold running performance is explained in detail. Apart from that, the effect of system parameters on cold working performance is investigated. In addition, this section includes the test procedure, fuel selection, test temperature, acceptance criteria, instrumentation requirements, and equipment and test plan. In the fifth section, which is the last section, the results of the tests are examined and compared in terms of pressure-time and temperature-time, and suggestions for improving the fuel system are mentioned. The main purpose of the fuel system is to deliver the required amount of atomized fuel to the combustion chamber of the engine. Because of that, the fuel needs to be pumped from the fuel tank to the high-pressure system and then pumped with very high pressures in order to be injected and sprayed in the injector nozzles. For this, two pumping operations need to be carried out, with the first operation the fuel will be transferred from the fuel tank to the high-pressure pump by the transfer pump and with the high pressure pump the pressure will be increased to required pressures. The higher injection pressures result in better atomization, which helps the fuel to burn more efficiently. Transfer pump pressures typically range from 0.3 to 8 bar, depending on the requirements of the system. The high pressures created by the injection system usually vary between 100 bar (old systems) and 2000 bar (new common rail systems), which together with the sensitizing system, increases the protection against abrasive dirt and water. The components of the fuel systems are; fuel tank, fuel transfer pump, low-pressure fuel lines, fuel injection pump, high-pressure fuel lines, injectors and fuel filters. The physical separation technologies can be classified with the major branches named Filtration, Sedimentation, and these two branches work by quite different mechanisms. Filtration works totally with particle or droplet size, such that particles below a certain size will pass through the barrier, while larger particles are kept on or in the filter media for later collection. Sedimentation works with the density of the particle or droplet and uses on the density difference between the particle and the fluid. It is the force of gravity working on this density that causes separation by sedimentation. With this method, of a solid can be extracted either from its suspension, or of a lighter solid from a heavier one. The contaminants of the diesel fuel are particulates, water, rusty water and air. The particulates which can cause failure on the engines includes abrasive dusts, water droplets, rust and organic materials. In addition, particles of grass and leaves can be an added contamination factor in agriculture. Silica or quartz is very abrasive materials and the common dust includes of 98% by weight of silica or quartz. Abrasive particles always can cause damage on fuel systems especially on transfer pumps and fuel injection parts. Generally, the most damaging particles for injection systems are in the 5 to 15 micron particle size. Abrasive particles cause frequently the scoring of the plungers of in-line pumps and unit injectors and the rotors of distributor pumps. The other critical areas are the wearing of the blades, the internal cam rings (transfer pump and high pressure cam), control mechanisms and metering edges of distributor pumps and they are sensitive to wear and often the first place that wear damage will occur. The water causes corrosion of ferrous metals and die cast Aluminium components in the fuel injection system, cavitation leading to nozzle tip failure. In addition, the lubricity can be reduced by the water and causing nozzle and pump plunger scoring. Air generally does not classifies as a contamination, but it is a form of contamination for sure. When air is drawn into a diesel fuel system, deterioration of engine performance will follow and be somewhat proportional to the amount of air that reaches the fuel injection system. If the enough air is present, the injection pumping system it will not be able to create enough pressure and it will not be possible to open the injector nozzle valves, so that the engine will not run. Electronically controlled fuel injection systems may also sense slugs of air as "no fuel" and shut the engine down. The most common problems related with air ingress are a rough running engine, loss of power or inability of the engine to start. The factors are which affect the cold start performance, fuel, fuel standards, working conditions, and the fuel system heating strategy. Because of that, when a fuel system design is needed, all the factors should be considered as well and a system should be designed in line with operating conditions. There is a lot of test procedure, which is being used for the validation of fuel in automotive industry, but most common and acceptable method for the fuel performance investigation is CFPP (Cold Filter Plugging Point). In most of the cases, it represents the behaviour of the fuel in vehicle conditions, but never fit 100% with the performance of the vehicle, because of that to consider the fuel system performance as well, a vehicle level testing needs to be conducted with specified fuel. In this review, a fuel system for medium commercial vehicles, which has common-rail fuel system on it have been, tested for different fuel system layouts. Firstly, it has been tested with current fuel system, which uses a recirculation flow from engine to heat dirty fuel in filter inside. With this test, it has been considered whether the recirculation is good enough to heat of the dirty side of filter. Because, with the low temperatures the fuel is starting to waxing and can block fuel filter easily and with a short time. The second test is conducted for the investigating of an additional fuel heater and its performance. The last test is conducted for an anti-freezing valve which recirculating the fuel from return fuel line to filter inside again and to aim heat the fuel inside of the filter to prevent cold start issues. Based on the test results, suggests&recommendations are provided for having a robust fuel system to survive in cold conditions.