Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2001-01-26
2002-06-11
Solis, Erick (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S299000
Reexamination Certificate
active
06401688
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system or method for enhanced auto-ignition in a gasoline internal combustion engine.
2. Description of Related Art
To improve thermal efficiency of gasoline internal combustion engines, lean burn is known to give enhanced thermal efficiency by reducing pumping losses and increasing ratio of specific heats. Flatly speaking, lean burn is known to give low fuel consumption and low NOx emissions. There is however a limit at which an engine can be operated with a lean air/fuel mixture because of misfire and combustion instability as a result of a slow burn. Known methods to extend the lean limit include improving ignitability of the mixture by enhancing the fuel preparation, for example using atomized fuel or vaporized fuel, and increasing the flame speed by introducing charge motion and turbulence in the air/fuel mixture. Finally, combustion by auto-ignition has been proposed for operating an engine with very lean air/fuel mixtures.
When certain conditions are met within a homogeneous charge of lean air/fuel mixture during low load operation, auto-ignition can occur wherein bulk combustion takes place initiated simultaneously from many ignition sites within the charge, resulting in very stable power output, very clean combustion and high thermal efficiency. NOx emission produced in controlled auto-ignition combustion is extremely low in comparison with spark ignition combustion based on propagating flame front and heterogeneous charge compression ignition combustion based on an attached diffusion flame. In the latter two cases represented by spark ignition engine and diesel engine, respectively, the burnt gas temperature is highly heterogeneous within the, charge with very high local temperature values creating high NOx emission. By contrast, in controlled auto-ignition combustion where the combustion is uniformly distributed throughout the charge from many ignition sites, the burnt gas temperature is substantially homogeneous with much lower local temperature values resulting in very low NOx emission.
Engines operating under controlled auto-ignition combustion have already been successfully demonstrated in two-stroke gasoline engines using a conventional compression ratio. U.S. Pat. No. 5,697,332 (=JP-A 7-71279) teaches an exhaust control valve to regulate the pressure in a cylinder during ascending stroke of a piston to achieve auto-ignition combustion of a two-stroke engine at optimum timing. It is believed that the high proportion of burnt gases remaining from the previous cycle, i.e., the residual content, within the engine combustion chamber is responsible for providing the hot charge temperature and active fuel radicals necessary to promote auto-ignition in a very lean air/fuel mixture. Besides, combustion temperature is low due to lean burn, causing a considerable reduction NOx emission. In four-stroke engines, because the residual content is low, auto-ignition is more difficult to achieve, but can be induced by heating the intake air to a high temperature or by significantly increasing the compression ratio.
In all the above cases, the range of engine speeds and loads in which controlled auto-ignition combustion can be achieved is relatively narrow. The fuel used also has a significant effect on the operating range, for example, diesel fuel and methanol fuel have wider auto-ignition ranges than gasoline fuel.
JP-A 11-236848 teaches a first fuel injection at a crank position more than 30 degrees before top dead center (TDC) position of compression stroke and a second fuel injection at a crank position near the TDC position to achieve controlled auto-ignition combustion in a diesel internal combustion engine. At the crank position of the first fuel injection, the temperature in the cylinder is still relatively low so that diesel fuel sprayed as the first fuel injection is not burnt but converted into flammable oxygen containing hydrocarbon due to low temperature oxidation reaction (partial oxidation of hydrocarbon molecules). At the crank position of the second fuel injection near the TDC of compression stroke, the temperature in the cylinder is sufficiently high enough to pyrolyze the gasoline sprayed as the second fuel injection, causing the gasoline to diffuse to make hydrogen due to pyrolysis. The hydrogen burns to elevate the temperature within the cylinder. This temperature elevation causes auto-ignition of flammable oxygen containing hydrocarbon (sprayed gasoline of the first fuel injection). This combustion promotes combustion of the sprayed gasoline of the second fuel injection.
According to this known technique, the injection quantity at the first fuel injection is held below 30% of the maximum injection quantity. Specifically, the injection quantity at the first fuel injection ranges from 10% to 20% of the maximum injection quantity. If the injection quantity at the first fuel injection exceeds 30% of the maximum fuel injection quantity, there occur fuel particles that are heated above the pyrolysis temperature by heat generated during low temperature oxidation reaction of the surrounding fuel., and hydrogen made due to the pyrolysis burns to cause early burn of sprayed gasoline at the first fuel injection. This accounts for why the injection quantity at the first fuel injection is held below 30% of the maximum injection quantity.
Apparently, this technique is intended for use in diesel internal combustion engines. Applying this technique to an auto-ignition gasoline internal combustion engine would pose the following problem.
It is now assumed that the total fuel quantity required per cycle is 60% of the maximum fuel injection quantity. In this case, spraying fuel as much as 10% of the maximum injection quantity at the first fuel injection timing will require spraying fuel as much as 50% of the maximum fuel quantity at the second fuel injection timing. As compared to diesel fuel, it is widely recognized that gasoline fuel is less ignitable, slow in reaction speed of cold temperature oxidation reaction, and least subject to pyrolysis including changes to make hydrogen. Accordingly, the fuel sprayed at the second fuel injection timing will not burn quickly. This sprayed fuel forms fuel rich mixture within a limited region of the combustion chamber, and this fuel rich mixture will burn simultaneously by auto-ignition after low temperature oxidation reaction. Under this combustion condition, increasing fuel quantity of the second injection may cause excessive pressure increase in cylinder and/or increased production of NOx.
JP-A 10-196424 teaches admission of ignition oil to achieve auto-ignition of mixture at or near TDC position of compression stroke. If, as the ignition oil, ignitable fuel is used other than gasoline fuel, dual fuel delivery systems are needed, resulting in increased complexity.
An object of the present invention is to provide a system or method for enhanced auto-ignition in an internal combustion engine.
SUMMARY OF THE INVENTION
In carrying out the present invention, a gasoline internal combustion engine is provided. The engine comprises:
a cylinder;
a reciprocating piston disposed in said cylinder to define a combustion chamber therein to perform an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke; and
a fuel injector directly communicating with said combustion chamber for spraying gasoline fuel,
a control arrangement being such that said fuel injector sprays a first injection quantity of gasoline fuel into said combustion chamber at first fuel injection timing, which falls in a range from the intake stroke to the first half of the compression stroke, thereby to form air/fuel mixture cloud that becomes a body of mixture as said piston moves from said first fuel injection timing toward a top dead center position of the compression stroke, and such that said fuel injector sprays a second injection quantity of gasoline fuel into said body of mixture at second fuel injection timing, which falls in the second half of the c
Aochi Eiji
Naitoh Ken
Teraji Atushi
Yoshizawa Koudai
Foley & Lardner
Nissan Motor Co,. Ltd.
Solis Erick
LandOfFree
Auto-ignition combustion management in internal combustion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Auto-ignition combustion management in internal combustion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Auto-ignition combustion management in internal combustion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2910682