Gasoline internal combustion engine

Details Gasoline internal combustion engine Gasoline internal combustion engine

2000-04-05

2001-10-30

Yuen, Henry C. (Department: 3747)

Internal-combustion engines

Combustion chamber means having fuel injection only

Combustible mixture stratification means

C123S299000, C123S305000, C123S430000

Reexamination Certificate

active

06308682

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a spark ignition gasoline internal combustion engine having means for separating the gasoline fuel into a higher boiling point fraction and a lower boiling point fraction, means for separately supplying the fractions to the combustion chambers of the engine, and means for introducing the separate fractions into the combustion chambers in such as a manner as to produce a stratified charge with the different fractions residing in different parts of the combustion chamber.
BACKGROUND OF THE INVENTION
Various proposals can be found in the prior art for stratifying the intake charge in an engine having one or more intake valves per cylinder by regulating the speed of the air flow along different regions of the skirts of the open valves during the induction stroke. The intake ports leading to the intake valves can be partitioned into separate passages and a flow control valve may regulate the relative air flows along the different passages by throttling one of the passages in order to direct the air flows from the other passages to different regions of the combustion chamber so as to promote charge stratification. Depending on the geometry of the intake system and the positioning of the flow control valve, the intake charge can be made to swirl (i.e. vortex about the cylinder axis) or tumble (i.e. vortex about an axis transverse to the cylinder axis). In the case of swirl, the intake charge is radially stratified with the flow from the throttled passage remaining at the centre of the vortex near the axis of the combustion chamber. In the case of tumble, the intake charge is stratified in layers lying in planes parallel to the cylinder axis.
It has also recently been proposed by the present Applicant in GB Patent Application No. 9716156.6 to provide a fuel vapour extraction system for a gasoline engine capable of continuously separating the fuel into a lighter vapour fraction and a heavier liquid fraction, the ratio of the two fractions being adjustable and the sum of the two fractions always matching the fuel demand from the engine. Such a vapour extraction system can continuously supply to the engine separately a vapour fraction that is easily ignitable and a liquid fraction that is more resistant to knock.
The Applicant's copending British Patent Appln. No. 9716829.8 relates to a gasoline spark ignition internal combustion engine having two or more intake passages supplying combustion air to each engine cylinder and a flow control valve regulating the air flow along one of the passages to each engine cylinder. The engine includes a vapour extraction system for separating the gasoline fuel into a lighter vapour fraction and a heavier liquid fraction. During part load operation of the engine, the air flow along the passage is throttled by the flow control valve, resulting in stratification of the intake charge in the combustion chamber of the cylinder with the gases flowing along the throttled passage remaining in the vicinity of a spark plug near the centre of the combustion chamber at the instant of spark ignition. At the same time, fuel from the vapour fraction is introduced into the intake passage throttled by the flow control valve to increase the concentration of the lighter fraction of the gasoline fuel in the vicinity of the spark plug at the instant of spark ignition.
The above copending patent application is only concerned with part load operation and is concerned with improving lean burn capability of the engine by improving the robustness of the lean combustion during part load operation. The proposal in this earlier patent is to revert to homogeneous charge preparation under full load operating conditions, because at that time the mixture is stoichiometric or rich and there is nothing to be gained in stratifying the charge distribution.
The Applicant's copending British Patent Appln. No. 9716157.4 also described an engine that uses charge stratification under part load and separates the gasoline fuel into a lighter and a heavier fraction. In this case, the lighter fraction is positioned away from the spark plug in order that it may spontaneously ignite but only after it has been compressed and heated by the advancing flame front from the part of the charge ignited by the spark. Here the objective is to produce controlled auto-ignition in order to reduce NOx emission and achieve very lean combustion. Once again, under full load operating conditions, the engine would be operated with a homogeneous charge as engine knock occurring under such conditions would damage the engine.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a spark ignition gasoline internal combustion engine having means for separating the gasoline fuel into a higher boiling point fraction and a lower boiling point fraction, means for separately supplying the fractions to the combustion chambers of the engine, and means for introducing the separate fractions into the combustion chambers in such as a manner as to produce a stratified charge with the different fractions residing in different parts of the combustion chamber, wherein the charge stratification under full load operating conditions of the engine is such that the lower boiling point fraction is ignited by the spark plug to burn first and initiate a flame that propagates through the combustible charge, and the higher boiling point fraction is concentrated in the end gas regions that are the last to be ignited by the advancing flame front and are most prone to knock.
Unlike the present invention, none of the earlier proposals above is concerned with the full load operating conditions. The present invention proposes running the engine with a stratified charge under full load conditions and at the same time ensuring that the higher boiling point fraction, which contains mostly aromatic components of the fuel that are highly resistant to knock, are concentrated in the end gas regions that are the most prone to knock. Furthermore, the lower boiling point fraction, which contains the lower octane rating paraffins and olefins, is burnt first and does not have the time and the temperature to achieve autoignition. As a result, the overall resistance to knock by the engine is increased. As it is the risk of knocking and engine damage under high load that places a limit on the engine compression ratio, the invention allows a higher compression ratio to be used safely with any given gasoline fuel, giving rise to improved efficiency and performance.
Unlike the earlier proposals, it is not essential to concentrate the lower boiling point fraction of the fuel in any one region of the combustion chamber and it is possible to distribute this lower boiling point fraction evenly throughout the combustion chamber provided only that under high load operating conditions, the higher boiling point fraction is concentrated in the end gas region.
Also unlike the earlier proposals, it is not sufficient that the higher boiling point fraction should reside away from the spark plug in the remoter region of the combustion chamber. In the present invention, it is essential to specifically locate the end gas regions which are most prone to knock and to concentrate the higher boiling point fraction at least in those regions. Typically the end gas region would reside in the part of the combustion chamber furthest away from the spark plug, but its exact position would depend on factors such as bulk charge motion displacing the ignition kernel away from the actual position of the spark gap, and local heating of the combustible charge by hot wall surfaces such as the exhaust valves. Because of these effects, even though the spark plug may be centrally located in a axially symmetrical combustion chamber, the end gas region most prone to knock may not be uniformly distributed around the entire circumference, but may reside in localised parts of the circumference. The exact position of such end gas regions will be best determined experimentally.
Because the higher boiling point fraction of t

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