Diesel injectors

Flow measurements for diesel injectors under a pressure drop of 0.6 bar. 

Montagne, X., D. Merrier and J.-C. Guibet (1987), "Fouling of automotive diesel injectors. Test procedure, influence of composition of diesel oil and additives". SAE paper No. 87-2118, International fuels and lubricants meeting, Toronto, Ontario. 

Plain-orifice atomizers are widely used for injecting liquids into a flow stream of air or gas. The injection may occur in a co-flow, a contra-flow, or a cross-flow stream. The best known application of plain-orifice atomizers is perhaps diesel injectors. This type of injectors is designed to provide a pulsed or intermittent supply of fuel to the combustion zone for each power stroke of the piston. As the air in the combustion zone is compressed by the piston to a high pressure, a very high pressure (83-103 MPa) is required to allow the fuel to penetrate into the combustion zone and disintegrate into a well-atomized spray. 

Thermal/oxidative effects contribute to viscosity change in the FZG test [77]. Diesel injector and FZG shear data were shown to correlate reasonably well in spite of evidence, based on GPC data, that the former appeared to be a purely mechanical process while the latter had a significant thermal and/or oxidation component. This may well relate back to the observation that a diesel injector shear process can best be simulated by assuming two steps [58], whilst others found that the FZG shear data appeared to involve three steps [59]. There is also a clear chemical bias indicating that the PMA thermal/oxidative component is less than that of other VI improvers in the study [77]. 

Baik, S., Blanchard, J. P., and Canadini, M. L., Development of Micro-Diesel Injector Nozzles via Microelectromehcanical Systems Technology and Effects rat Spray Characteristics, J. Eng. Gas Turbines Power, vol. 125, April 2003, pp. 427-434. 

Surfactants are used in fuel applications to prevent fuel injector deposits, intake valve and exhaust valve deposits, combustion chamber deposits [2,3], injector deposits of direct gasoline injector systems [4,5] and high-pressure diesel injector systems [6], and low-temperature intake valve deposits [7]. 

Case study 2 - Assembly and test of diesel injector units Product and customer requirements... 

The necessity of carrying out injection at high pressure and the atomization into fine droplets using an injector imposes very precise volatility characteristics for the diesel fuel. French and European specifications have established two criteria for minimum and maximum volatility therefore, the distilled fraction in volume % should be ... 

The level of injector fouling is most often illustrated in terms of residual flow (RF) expressed as a percentage of the flow under new conditions for a given needle lift. An RF on the order of 20% for a lift of 0.1 mm is a good compromise. This level may not be achieved with certain aromatic or naphthenic diesel fuels. The best recourse is then detergent additive addition. 

Diesel engine injector fouling. Residual flow (RF) for different additive levels. ... 

The role of detergent additives is to maintain clean injectors so as to insure good distribution of diesel fuel in the cylinder. The structure of these compounds is similar to that of detergents for gasoline engine admission systems. Commercialized compounds are from the succinimide family (see Figure 9.1). 

Viscosity. For optimum performance of diesel engine injector pumps, the fuel should have the proper viscosity. Too low viscosity results in excessive injector wear and leakage. Viscosity that is too high may cause poor atomisation of the fuel upon injection into the cylinders. 

Detergent Additives. Diesel engine deposits ate most troublesome in the fuel dehvery system, ie, the fuel pump and both fuel side and combustion side of the injectors. Small clearances and high pressures mean that even small amounts of deposits have the potential to cause maldistribution and poor atomization in the combustion chamber. The same types of additives used in gasoline ate used in diesel fuel. Low molecular weight amines can also provide some corrosion inhibition as well as some color stabilization. Whereas detergents have been shown to be effective in certain tests, the benefit in widespread use is not fully agreed upon (77). 

All diesel fuels tend to contain trace water, expressed in parts per million (ppm). With the veiy high fuel injection pressures now used in electronically controlled diesel engine, fuel-filter/water separators are widely used, since water allowed to circulate freely through the injection system can result in seizure of components and erosion of injector orifice holes, and in extreme cases the high compressibility factor of water can blow the tip off of the fuel injector. 

Fuel injection, diesel, 70 60-61 Fuel injection systems, 70 51 Fuel injector detergents, 72 408 409 Fuel metering system dynamic (lag time), 70 50... 

MMD = 6dfj Re 0 15 Liquid jet from a diesel-type injector into quiescent air 1000 < Rez < 12000 Panasenkov(435]... 

SMD = CpA Vl (pm), c=25.1,23.9, 22.4 for pintle,hole,throttiingpiulle nozzles, resp. Liquid jet from a diesel-type injector into quiescent air, A-Pf. (MPa), Pa (kg/rn3), (mm3/stroke) HiroyasuA Kadotil3 ]... 

The addition of ethanol to diesel lowers fuel viscosity and lubricity. Lower fuel viscosities lead to greater pump and injector leakage, reducing maximum fuel delivery and hence power output. Hot start problems may also be encountered as insufficient fuel may be injected at cranking speed when fuel leakage in the high-pressure pump is amplified because of the reduced viscosity of the hot fuel. 

A critical safety issue of using diesel-ethanol blends relates to flashpoint and flammability. E-diesel blends containing 10-15% ethanol have the vapor pressure and flammability limits of ethanol. This means that ethanol concentrations in enclosed spaces such as fuel storage and vehicle fuel tanks are flammable over the temperature range 13-42 °C. Thus, there are higher risks of fire and explosion than with diesel fuel, or even gasoline. Other vehicle performance-related concerns are (a) a decreased maximum power (b) an increased incidence of fuel pump vapor lock and (c) a reduced fuel pump and fuel injector life due to the decreased lubricity of ethanol. 

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