Fuel Injection Information

This reversion pressure condition can (1) limit the amount of fresh air/fuel mixture passing into me engine and (2) cause a degree of mixture “contamination” because of exhaust gas residue from poor scavenge of cylinder evacuation of combustion by-products. Air/fuel mixtures are only going to burn once, so rt s kinda nice to get as much combustion after-stuff out of the engine as possible before the fresh material goes in.
Both of these two conditions atomization efficiency and injected mixture timing) are known problems of conventional carburetors, and a *ell-designed fuel injection system improves the ability to solve them both. So with this much of an introduction to the failings of carburetion, let’s see what fuel injection systems can do to improve the situation.
By at least one definition, a fuel injection system is intended to inject a specific amount of fuel at a particular time into an engine’s induction system or combustion chambers. Also, the system should provide good fuel atomization and distribution of either fuel or air/fuel mixtures, depending

upon the location of injected fuel. Some systems (like the Bendix version used on Cadillac Seville engines) have injected fuel loose in the intake ports and/or manifold, since four injectors deliver fuel at one time. Other systems (like typical diesel engines) inject fuel directly into the combustion chamber, timing fuel delivery so that ignition is the result of compression pressure and not spark initiated.
Fundamentally, you could classify injection systems as (1) solid fuel injection (2) air injection. Solid fuel injection (probably the most common today) injects fuel only, and at a specific time relative to piston position (usually toward the later stages of the compression stroke). Air injection systems, as you probably figured, provide some amount of air with the injected fuel, are more complicated than solid fuel systems, and use high-pressure compressed air to “drive” the mixture into the engine’s cylinders.
In the solid fuel injection category, there are “continuous” and “timed” systems. The continuous method causes fuel to exist in liquid state in the intake manifold or behind intake valves (at some point during engine operation), whereas the timed systems inject fuel normally during the first half of the intake stroke (usually beginning shortly after the exhaust valve closes and ending no later than 100-110 degrees after top dead center of the intake stroke).
Timed systems can be designed to deliver fuel based on mechanical release of fuel (belt-drive, cam-operated, etc.) or electronic controls. And with the degree of sophistication offered by contemporary electronics technology, this method seems to offer greater control of fuel and engine efficiency. This is especially true of electronic fuel injection systems capable of including such variables as intake manifold vacuum, engine rpm, ignition timing, outside air pressure (altitude compensation), and engine coolant temperatures in the overall determination of how much fuel should be delivered to the engine based on optimum fuel economy and driveability.

C. Here are three common types of Bosch-designed fuel injector nozzles. The multiple-hole version (a) uses a tapered needle that is withdrawn from its seat for fuel delivery. The throttling nozzle (b) has a deflector cone just below the needle tip to improve fuel atomization. And the straight-tip pintle nozzle design (c) relies on sharp-edged discharge orifice openings and high fuel pressure to provide good atomized fuel. D. This for all you guys in 10th grade physics. Since air and fuel are of different weights (mass) for equal volumes, each will have different flowing energy at any given flow velocity. At point (1), both air and fuel are moving at the same velocity (speed). At points (2) and (3), a change in flow direction is required. The air particle is less affected by centrifugal forces and tends to slow down and make the turn more easily than the heavier fuel particle. By the time each gets to point (4), the fuel particle is traveling faster than the air particle (and is more influenced by centrifugal forces). And this is the basis for air/fuel mixture separation in engines for which mixtures must pass some distance from mixing valve (carburetor or upstream injector) to combustion chamber. Direct cylinder (or port) injection helps solve this fundamental problem of lost power and reduced fuel economy.

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