Fuel injector

Fig. 12. Methanol and coach fleet cumulative distance driven before fuel injector failure, where I...

Ferroelectric thin films have not, as of this writing, been commercialized. Demand for PTC ferroelectrics has been decreasing rapidly. Wide usage of the fuel injector in automobiles and other types of composite PTC devices is the main reason. 

Parts made from fluoroelastomers ate used ia appHcations that justify their high cost, usually where the maintenance and replacement costs are high enough to offset the initial cost of the part. These include automotive appHcations such as valve stem seals, fuel injector components, radiator, crankcase and transmission seals, and carburetor needle tips. Numerous seals and gaskets in the marine, oilfield, and chemical processing industries employ fluoroelastomers. In addition, many hoses in the automotive and chemical industry are made entirely of fluoroelastomer compounds or have a veneer of the fluoroelastomer as a barrier exposed to the harsh environment. Seals and gaskets in military appHcations and the binder for flares and missile appHcations ate made with fluoroelastomers. 

Liquid fuel is injected through a pressure-atomizing or an air-blast nozzle. This spray is sheared by air streams into laminae and droplets that vaporize and bum. Because the atomization process is so important for subsequent mixing and burning, fuel-injector design is as critical as fuel properties. Figure 5 is a schematic of the processes occurring in a typical combustor. 

Main fuel injector. This unit is designed to deliver a fuel-air mixture to the catalyst that is uniform in composition, temperature, and velocity. A multi-venturi tube (MVT) fuel injection system was developed by GE specifically for this purpose. It consists of 93 individual venturi tubes arrayed across the flow path, with four fuel injection orifices at the throat of each venturi. 

The fuel is delivered to the engine by one of two methods recirculating or retum-less. In a recirculation system, as is shown with dashed lines in Fig. 4, the engine fuel injectors draw a portion of the fuel being delivered in the fuel rail, and the... 

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. 

Such tight mixture control is beyond the capability of the traditional carburetor. Consequently, after sorting through a number of alternatives, industry has settled on closed-loop-controlled port-fuel injection. Typically, an electronically controlled fuel injector is mounted in the intake port to each cylinder. A sensor in the air intake system tells an onboard computer what the airdow rate is, and the computer tells the fuel injectors how much fuel to inject for a stoichiometric ratio. An oxygen sensor checks the oxygen content in the exliaust stream and tells the computer to make a correction if the air/fuel ratio has drifted outside the desired range. This closed-loop control avoids unnecessary use ot an inefficient rich mixture during vehicle cruise. 

Case study B4 Automotive components, fuel injectors... 

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... 

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. 

Cardiovascular Effects. Two case studies were found that reported mild hypertension in humans from acute inhalation exposures to fuel oils. Mild hypertension was noted for 4 days in one of two individuals following a 1-hour exposure to JP-5 vapor while flying a small airplane (Porter 1990). Delayed mild hypertension was also noted in a man who was exposed to diesel fuel vapor for 10 days while driving a truck with a fuel injector leak (Reidenberg et al. 1964). The concentration of vapor was not reported in either study. Palpitations were noted in workers chronically exposed to jet fuel according to one epidemiological study (Knave et al. 1978). The limitations of this study are discussed in detail in Section 2.2.1.2 under Respiratory Effects. 

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