DIRECT-INJECTION CREATES MORE EFFICIENT GASOLINE ENGINES

2001 Cleaner, Safer, Sooner releases

Snides Remarks: Notice the date obn this release...this and others showed up in my e mail in response to my last article., Thanks whoever.

DEARBORN, MICHIGAN, AUGUST 21, 2001- Direct injection technology originally developed for diesel engines has shown potential fuel economy improvements of approximately 20 percent when adapted by Ford Motor Company engineers for gasoline engines.

This technology - called DISI for direct injection spark ignition - is being tested in a 1.1-liter three-cylinder gasoline engine that achieves 70 hp.

In primarily urban driving, this translates to a 21 percent improvement in fuel economy from the engine technology alone. In mixed urban and highway driving, the engine is expected to improve gas mileage by 10 to 15 percent. Combining DISI with other new technologies that take advantage of its low-RPM efficiency should produce even greater savings.

The engine is also expected to meet or exceed European Stage IV emissions standards - that take effect in 2005.

How it Works

In a direct injection engine, the injection nozzle is located inside the combustion chamber, rather than in the induction pipe as in multi-port or throttle-body fuel injection.

With a conventional fuel injected engine, all cylinders are supplied with a mist-like mixture of air and fuel, at a constant 14.7:1 ratio. One or more injector nozzles spray fuel into the air stream being fed to the intake valves. This spray is mixed with air during the intake stroke and flushed into the cylinder, where it is ignited by the spark plug.

The throttle valve determines how much of the air-fuel mixture enters each cylinder. A closed throttle valve means little air in the engine, and thus a small amount of injected fuel, while an open throttle means a lot of air in the engine, equating to a lot of fuel.

Under traditional technology, the air-fuel mixture inside the cylinder can't deviate very much from the optimum 14.7:1 ratio of air to fuel. In particular, air-fuel mixtures that are too lean simply won't ignite.

DISI engine technology uses so-called stratified charging to overcome this limitation.

With DISI, the spark plug is surrounded by a relatively small, precisely shaped volume of ignitable air-fuel mixture that results when fuel is sprayed toward the spark plug just before ignition. Only the area directly around the spark plug, at the top of the cylinder, contains air-fuel mixture. Other areas inside the combustion chamber merely contain air or recirculated exhaust gas.

This stratification of the charge allows the new DISI engine to burn mixtures with a much higher rate of air than conventional lean-mix engines. With the Ford DISI engine, the fuel-air ratio can increase to 60 parts of air (instead of 14.7) for every part of fuel.

The cushion of non-combustible gas around the combustion chamber also means that less combustion heat has to be evacuated. This improves the thermal efficiency of the engine.

Fuel is injected into the cylinder. The shaped piston crown guides the air/fuel mix to the spark plug.

As the spark plug fires, igniting the mixture, surrounding areas contain only air or recirculated gases, forming an insulating cushion at the cylinder walls and cylinder head.

Another factor contributing to improved fuel economy is the ability to increase the compression ratio from about 10:1, as is normal, to approximately 11.7:1 without the need for premium fuel, because direct injection reduces the tendency of engine knock. The higher compression ratio alone increases efficiency by about two percent.

The DISI charge stratification process works best at low and medium loads in the lower half of the engine speed range, where traditional gasoline engines are least efficient.

The major fuel reduction potential of 21 percent is realized in the urban driving cycle because, under these driving conditions, the DISI engine operates in a stratified-lean mode most of the time.

Synergistic Technology

Changes in the coolant system also could help to improve fuel economy for a vehicle equipped with the DISI engine.

A typical feature of DI engine thermodynamics is the difference in thermal losses, depending on whether the engine is operated in the economy or full-load mode. In the economy mode, an insulating blanket of air and recirculated exhaust gas helps keep heat away from the cylinder walls and head. In the high-powered mode, more heat is released.

A new control system for the coolant circuit could shut off the fan motor over a longer period of time or reduce the operating speed of the water pump, during economy mode operation. Either would reduce operating drag on the engine, and improve economy.

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