High pressure injectors

When gas molecules under high pressure are allowed to escape and expand, they release kinetic energy. This energy has been harnessed to benefit human health by powering high-pressure injectors, better known as jet injectors. 

Medium high-pressure g.I.c. does require more sophisticated apparatus as is shown in the flow diagram of Figure 4. It must include a high-pressure injector, pressure-control values, special metal-to-glass seals, and a flow meter capable of operating at pressures of 1200 kPa. These will be discussed later in this section. 

Common-Rail System and High-Pressure Injector... 

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 ... 

For liquid chromatography, a sample of the mixture solution is injected through a loop injector which allows a quantity of the solution to be placed in a small tubular loop at atmospheric pressure. By manipulating a valve, the high-pressure flow of solvent to the column is diverted through the loop, carrying the sample with it (Figure 35.5). 

A typical loop injector showing the sampling position with pressurized solvent flowing through one loop onto the column and the sample solution placed in the other loop at atmospheric pressure. Rotation of the loop carrier through 180° puts the sample into the liquid flow at high pressure with only momentary change in pressure in the system. 

The collection of particles larger than 1—2 p.m in Hquid ejector venturis has been discussed (285). High pressure water induces the flow of gas, but power costs for Hquid pumping can be high because motive efficiency of jet ejectors is usually less than 10%. Improvements (286) to Hquid injectors allow capture of submicrometer particles by using a superheated hot (200°C) water jet at pressures of 6,900—27,600 kPa (1000—4000 psi) which flashes as it issues from the nozzle. For 99% coUection, hot water rate varies from 0.4 kg/1000 m for 1-p.m particles to 0.6 kg/1000 m for 0.3-p.m particles. 

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). 

For higher pressures, stopped flow injection has been used in which a valve releases the pressure in the column to atmosphere, at which point syringe injection at the top of the column (without septum) takes place. There has, however, been a trend in recent years to use valve injectors because of their generally high pressure capabilities and their ability to deliver large... 

The cost and impact on injectors are key concerns for feedstock preparation. There are difficulties in injecting alternative materials into high-pressure gasifiers. 

A high-speed injector is required in supercritical fluid chromatography. This is to prevent loss of pressure during the injection process. 

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. 

The decrease in the mean droplet size with increasing liquid injection pressure may be attributed to two effects. First, the high pressure-drop across the exit orifice makes the process more like a pressure atomization at high pressure. Second, the liquid is squeezed into fine ligaments as it flows through the injector orifice, and the ligaments are shattered into small droplets by the explosion downstream of the nozzle exit. 

As mentioned previously, introducing the sample to the flowing mobile phase at the head of the column is a special problem in HPLC due to the high pressure of the system and the fact that the liquid mobile phase may chemically attack a rubber septum. For these reasons, the use of the so-called loop injector is the most common method for sample introduction. 

A common cause of unusually high pressure is a plugged in-line filter. In-line filters are found at the very beginning of the flow line in the mobile phase reservoir, immediately before and/or after the injector, and just ahead of the column. With time, they can become plugged due to particles that are filtered out (particles can appear in the mobile phase and sample even if they were filtered ahead of time), and thus the pressure required to sustain a given flow rate can become quite high. The solution to this problem is to backflush the filters with solvent or clean them with a nitric acid solution in an ultrasonic bath. 

Other causes of unusually high pressure are an injector blockage, mismatched mobile and stationary phases, and a flow rate that is simply too high. An injector that is left in a position between load and inject can also cause a high pressure, since the pump is pumping but there can be no flow. 

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. 

Injectors introduce the sample into the mobile phase under high pressure. There are several approaches to injection in HPLC, such as syringe injection via septum, a combination of a septum and syringe or a valve injection. Valve injection is the method of preference in up-to-date HPLC instrumentation. 

Autosampler or injector—replace rotor seal in injector valve or high-pressure needle seal pack, sampling needle, and sampling syringe. 

Detergents used in diesel fuel help to control deposit formation on fuel injector nozzles and act to prevent corrosion of the nozzle orifices. Diesel fuel detergents also aid in preventing deposit and gum formation on high-pressure fuel injector parts. 

High-pressure diesel fuel injection systems contain expensive and sophisticated components. The high-pressure pump and injector are the key components to ensuring proper fuel management within the diesel engine. Clearances and tolerances between moving parts of the fuel pump are quite fine. Even a small amount of deposit, contamination, or corrosion can significantly alter the efficient performance of the fuel injection system. 

A typical fuel injection system is composed of the following components fuel tank, injection pump, mechanical or electronic governor, timing device, fuel supply pump, high-pressure fuel injection lines, and fuel injectors. The high-pressure fuel injection pump is the core of the fuel injection system. The in-line pump and distributor pump are the most common in fuel systems. 

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