Fuel Injection Information

Exotic as it may seem, this approach to fuel delivery solves many basic problems of good combustion efficiency. and it also applies to stock engines

Understand how the conditioning of air and fuel can affect overall engine performance. We’ve also touched on the importance of when air/fuel mixtures enter an engine’s cylinders, how they are best burned (oxidized), and some of the better ways of exiting exhaust gases. There has even been some mention of what happens when fuel particle size varies (from one droplet to the next) and the improvement in combustion efficiency when some measure of control is provided regarding atomization of fuel.

Carburetors, it has been suggested, are a form of compromise in comparing the best theoretical way to introduce fuel to an engine in the most cost effective way (just a fancy “accountant’s” way of saying does it cost more than it’s worth). But with the rising cost of today’s fuel, and the roads not getting any shorter, fuel economy is of increasing concern.
Fuel injection techniques offer some interesting solutions to the
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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
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Fallout from one more moon shot, as applied to the automotive industry, will probably require you to say “good morning” to your car just to get it started in the morning.
Two other aspects of fuel injection, at this point, are worth understanding. One is the point at which fuel is injected relative to piston position (“timing” of the injected mixture) and the other is how long this injection should last (“duration” of the injected charge).
Ideally, fuel should be introduced in the inlet air stream while air is moving toward the cylinder. In fuel injection systems where fuel is injected outside the combustion chamber, this is normally about 30-45 crankshaft degrees after top dead center of the intake stroke. By this time, any residual exhaust pressure (reversion) passing out of the cylinder and back into the intake system has subsided and fresh air is moving into the cylinder. It doesn’t mean that some amount of exhaust gas won’t still be in the cylinder; it just means the injected fuel has little chance of being blown back into the intake system once sprayed into the airstream. Read the rest of this entry »

If too much fuel is provided too quickly, detonation (as a result of excessively high combustion pressures) will follow, with power loss and engine damage distinct possibilities. Diesel truck engines are particular applications of this version of fuel injection, as are most diesels where the engine is required to “run in detonation” (as Jr. Johnson describes his pending Grand National Olds-mobile race engine project using the ability of diesel cylinder blocks to withstand the rigors of NASCAR racing). And while you’re wondering why that little tidbit appeared in a Shop Series, we will too. But it’s fact.
Functionally, a conventional fuel injection system will consist of the following pieces: an injector nozzle for each of the engine’s cylinders (or more than one nozzle per cylinder as in the case of many injected supercharged engines), a system of fuel lines and pumps for which higher-than-carbureted engine fuel pressure will be carried (30-80 pounds of pressure is common), mechanical or electronic fuel injection timing (for timed systems) or flow (if continuous fuel delivery), and some means for throttling the amount of air going into the engine.
Principal advantages are improved quality of air/fuel mixtures just ahead of or inside the combustion chamber, either before or during combustion.

By injecting fuel directly into the engine’s combustion chamber, less fuel will be left in the induction system. And since air can be passed more efficiently than fuel into an engine’s cylinders, late fuel entry is best achieved by fuel injection near the combustion chamber.
All this good theory is nice. But what we’re trying to achieve is the proper mixture of air and fuel (under favorable conditions of combustion pressure and heat) in the most-used range of engine rpm. If the engine is a wide-open-throttle race piece, little consideration should be given for light-throttle acceleration and/or idle characteristics. But if you’re faced with sub-zero cold-starts on your way to school or work, who cares how well an injection system works at 8400 rpm on the back straight at Riverside?
One thing’s for certain. With the present concern for fuel economy and the advantages possible from a correctly designed fuel injection (or electronically monitored) system, conventional carburetion may be in for some serious redesign. And for sure, we aren’t fueling.

REVIEW QUESTIONS: True or False
1. Carburetors tend to atomize liquid fuel into smaller particle sizes than conventional fuel injection systems.
2. Injector nozzle fuel pressure has little to do with the size of atomized fuel particles entering the airstream or combustion chamber.
3. Regardless of injector nozzle atomization efficiency, large fuel droplets burn more quickly than smaller ones.
4. Fuel injection systems that inject fuel directly into the combustion chamber usually provide less performance and economy than systems that inject fuel into the intake manifold or intake port.
5. Timed injection means fuel delivery based on precise matching of the ignition system’s rate of timing advance.
6. Solid fuel injection systems inject fuel into the engine’s cylinders at a time related to piston position, usually during the last half of the intake stroke.
7. One disadvantage of electronic fuel injection is that it cannot compensate for variations in altitude and incoming air temperature.
8. Fuel passing out of an injector nozzle is atomized primarily because of fuel particle friction with the air it is entering.
9. For optimum fuel delivery into an engine’s cylinders, it is best to time injector operation with the point at which the intake valve just begins to open.
10. Injector nozzle deflector cones (on the discharge ends of injector needles) are used to improve fuel atomization.
11. As air and fuel travel through an induction system, fuel has less kinetic energy than air, thus enabling it to turn corners more easily than air.
12. Solid fuel injection systems inject fuel with no particular regard to piston position.
13. Air injection systems rely on high-pressure fuel and low-pressure air to supply an engine with the proper air/fuel mixtures.
14. This month, answers to some of the True or False questions came from study of the graphics part of the story.