Internal combustion engine

Details Internal combustion engine Internal combustion engine

1994-05-17

1996-06-11

Heyman, Leonard E.

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

60304, 60305, 60307, F01N 322

Patent

active

055244343

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to an internal combustion engine in which liquid fuel is introduced prior to the charge entering the combustion chambers.
In petrol engines in which mixture preparation takes place outside the combustion chambers, for example by means of a carburettor or fuel injectors supplying fuel into the intake manifold or intake ports, engine deceleration is accompanied by a rich incomplete combustion because some fuel is stored in the intake system and this is stripped off from the wetted surface of the walls of the intake manifold and intake ports during the deceleration mode by the high manifold depression. Even if the fuel supply is cut-off completely during the deceleration mode, a sudden excursion of exhaust emissions will still occur since the engine air supply has been restricted and the stored fuel is burnt in the combustion chamber with insufficient air. The duration of the excursion is relatively short as the quantity of the stored fuel is finite and once used up there is no more fuel but nevertheless unburnt hydrocarbons are released to atmosphere during these periods as there is not sufficient oxygen in the exhaust system to allow them to be oxidised, even in a catalytic converter.
The present invention seeks to cut down on this source of air pollution by reducing the unburnt hydrocarbon content of the exhaust gases during deceleration modes.
According to the present invention, there is provided an internal combustion engine in which liquid fuel is introduced into the air intake system prior to the charge entering the combustion chambers and which is mounted in a vehicle having an air scoop acting as a source of ram air pressurised by the movement of the vehicle, characterised in that the ram air is fed into the exhaust system of the engine by way of an isolation valve which is opened only during engine deceleration modes.
In order to complete the combustion of the unburnt hydrocarbons in the exhaust system, a source of additional oxygen is required. Hitherto, various proposals have been made to add air into the exhaust system under different operating conditions. For this purpose, pulse air system have been put forward which rely on the pulsation of the gases in the exhaust manifold to draw in air during negative pressure parts of the cycles but such system do not draw in air during deceleration mode as the pressure pulse amplitude is severely attenuated at such times. Electrically driven air pumps have also been proposed but these have a slow response time and cannot be brought into operation sufficiently rapidly to respond to the engine entering a deceleration mode. Of course, if a continuously driven air compressor is available in the vehicle for some other reason, for example to assist fuel atomisation in a fuel injection system, its air may be diverted for this purpose but it is not an effective solution to provide a compressor exclusively for this purpose as the cost and energy consumption would be prohibitive.
The present invention provides a convenient, reliable and inexpensive air supply for counteracting hydrocarbon emissions during deceleration modes only having as a moving part a valve to admit air into the exhaust system when deceleration has been detected. The valve may be operated electrically or by intake manifold vacuum, the latter being particularly high when the engine is overrunning.
The invention takes advantage of the fact that during deceleration modes, the exhaust back pressure is minimal and only a small positive pressure is needed to ram air into the exhaust system. Furthermore, deceleration modes responsible for atmospheric pollution occur mostly when the vehicle is in motion, at which times the ram air pressure is always present.
The ram air pressure will be present whenever the vehicle is in motion and it is possible not to activate the isolation valve when the vehicle is travelling below a preset speed to avoid exhaust gases being expelled without passing through the exhaust system. Alternatively the valve may be connected in series with a weak

REFERENCES:
patent: 3390520 (1968-07-01), Mattson
patent: 3470689 (1969-10-01), Gurr
patent: 4177640 (1979-12-01), Kuroda
patent: 4383408 (1983-05-01), Vjihashi et al.
patent: 4583363 (1986-04-01), Urushidani et al.

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