Fuel Injection - Why More Modern Systems

In an earlier blog I listed a variety of reasons fuel injection systems were developed. Much of the following information is from Wikipedia.

The major one is elimination of harmful emissions. The ultimate combustion goal is to match each molecule of fuel with a corresponding number of molecules of oxygen so that neither has any molecules remaining after combustion in the engine and catalytic converter. If this is achieved you have reached California's goal for cars.

Typically you have an Engine Control Unit (ECU) which monitors the air and fuel mixtures via one or more sensors. One of the most critical sensors is in the exhaust gas. The actual injector is simple in theory. It's just a valve that opens and allows fuel to flow into the engine. Where the valve is place, how long it is open, when it opens etc. are some of the critical factors that must be calculated.

There have been various different types of Injection systems. One of the earliest was the Bosch K-Jetronic which was a Continuous Injection System. This was introduced in 1974, and it is the system used on my 1984 Ferrari 308. Gasoline is pumped from the fuel tank to a large control valve called a fuel distributor, which separates the single fuel supply pipe from the tank into smaller pipes, one for each injector. The injectors are simple spring-loaded check valves with nozzles; once fuel system pressure becomes high enough to overcome the counterspring, the injectors begin spraying. K-Jetronic was used for many years between 1974 and the mid 1990s.

Another approach was when General Motors implemented a system called "central port injection" (CPI) or "central port fuel injection" (CPFI). It uses tubes with poppet valves from a central injector to spray fuel at each intake port rather than the central throttle-body.

If you have a newer car then you probably are using a Multi-point system. Multi-point fuel injection injects fuel into the intake port just upstream of the cylinder's intake valve, rather than at a central point within an intake manifold, referred to as SPFI, or single point fuel injection. MPFI (or just MPI) systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke, batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke, or Simultaneous, in which fuel is injected at the same time to all the cylinders.

All modern EFI systems utilize sequential MPFI.

In my first blog I mentioned that fuel injection systems in automobiles were used in racing cars. This technology then moved to street vehicles. This progression is continuing. Race cars (for example Formula One) began using a system called Direct Injection. Many diesel engines use this approach also. The injection nozzle is placed inside the combustion chamber and the piston incorporates a depression (often toroidal) where initial combustion takes place. Direct injection diesel engines are generally more efficient and cleaner than indirect injection engines.

This is the next step for gasoline powered cars. You will begin to see it implemented on higher end exotics like Ferrari and Lamborghini and as the volume increases the technology will move to more and more stock cars. It gives the car more power at the correct time, and the efficiency is becoming more important as fuel prices rise and we move to greener vehicles.

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