Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-05-02
2001-10-23
Solis, Erick (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S090150, C701S104000
Reexamination Certificate
active
06305364
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the fuelling of an internal combustion and application thereof to both gasoline and diesel engines.
BACKGROUND OF THE INVENTION
It has already been proposed to pre-condition fuel before it is injected into the combustion chambers of an engine by heating the fuel. Hitherto, this has been achieved using heat present in external EGR (exhaust gas recirculation) gases by injecting the fuel into an EGR pipe leading from the exhaust system to the intake system. This could only be achieved by means of additional equipment such as a fuel injector and a reaction chamber in the exhaust recirculation system.
SUMMARY OF THE INVENTION
A principal object of the present invention is to make use of processes that normally take place in conventional four stroke internal combustion engines to enhance fuel preparation and to produce more reactive radicals in the intake charge at the commencement of combustion in order to improve the ignitability of the fuel and air mixture.
According to one aspect of the present invention, there is provided a four stroke internal combustion engine in which, at least during certain pre-defined engine operating conditions, the intake and exhaust valves are open simultaneously to enhance internal exhaust gas recirculation (EGR) by forcing a substantial quantity of exhaust gases back into the intake ports, the engine having a fuel injection system with fuel injectors arranged in the intake ports, a variable valve timing system operative, at least during the said engine operating conditions, to prolong the valve overlap period when the intake and exhaust valves are simultaneously open, and a fuel control means for controlling the timing of the fuel injectors to introduce substantially all of the injected fuel directly into the back flow of internal EGR gases during the extended or prolonged valve overlap period, the fuel being thermally conditioned by the hot internal EGR gases before being admitted into the combustion chamber during the subsequent intake stroke.
In order to determine the optimum timing for port fuel injection, it has previously been attempted to vary the timing of fuel injection in relation to the operating cycle of the engine. By such experimentation, it has been determined that when the fuel is injected into the intake ports with the intake valves closed, the fuel is deposited on the hot walls of the intake ports and is heated and preconditioned before being drawn into the engine. This resulted in more reliable ignition and more complete combustion. When fuel is injected into the intake ports with the intake valves open, on the other hand, it has been found that the resulting combustion is not satisfactory because of poor mixing and less reliable ignition. In this case, the fuel has little time to be heated and is entrained by the intake air and deposited on the walls of the combustion chamber.
While attempting all possible injection timings, it is likely that it was attempted to inject fuel during the very brief valve overlap period. However, because this period is normally of much shorter duration than the fuel injection period, the advantageous effect achieved in the present invention has not previously been recognised. The important difference to note is that in the present invention special steps need to be taken to prolong the valve overlap period in order to ensure that substantially all of the injected fuel can be timed to be introduced into the hot EGR gases during the valve overlap period.
According to a second aspect of the present invention, there is provided a four stroke internal combustion engine in which, at least during certain engine operating conditions, the intake and exhaust valves are open simultaneously to enhance internal exhaust gas recirculation by forcing a substantial quantity of hot exhaust gases back into the intake ports, the engine having a fuel injection system with fuel injectors arranged in the combustion chambers, a variable valve timing system operative, at least during the said engine operating conditions, to prolong the valve overlap period when the intake and exhaust valves are simultaneously open, fuel control means for controlling the injection timing of the fuel injectors to introduce substantially all of the injected fuel directly into the residual gases in the combustion chambers during the extended valve overlap period, and pressure control means for creating a pressure drop from the exhaust ports towards the intake ports during the valve overlap period to ensure that the injected fuel does not pass out of the combustion chamber through the open exhaust valve, the fuel being thermally conditioned by the hot residual gases before the commencement of the subsequent intake stroke.
The second aspect of the invention differs from the first in that the fuel is injected directly into the combustion chambers rather than the intake ports. For this reason, it is necessary to take steps to control the pressures in the intake and exhaust ports to ensure that the injected fuel remains in the combustion chamber and is not allowed to escape through the open exhaust valve before it has been burnt.
In both its aspects, the present invention sets out to achieve thermal conditioning of the injected fuel by ensuring that it is heated by the hot burnt gases from the previous operating cycle before commencement of the subsequent intake stroke, thereby improving the ignitability of the fuel in the subsequent operating cycle. This can be used to achieve a more robust ignition during lean burn operation or to promote spontaneous ignition during low and medium load operation in order to reduce NOx emissions.
The means for ensuring sufficient pressure drop from the exhaust ports towards the intake ports may be an intake throttle for restricting the intake air flow and reducing the pressure in the intake ports. Alternatively the means may be an exhaust throttle for restricting the exhaust gas flow and increasing the pressure in the exhaust ports. As a further alternative, an intake throttle and an exhaust throttle may be used in combination.
The present invention is applicable to both gasoline and diesel fuels and is advantageous in promoting thermal pre-conditioning of the fuel by the hot residual gases retained in the cylinder thus improving the ignitability of the fuel when it is burnt in the immediately following engine cycle.
For a spark ignition engine, the lean burn capability of the engine can be significantly extended resulting in lower fuel consumption and lower exhaust emissions.
Under certain conditions, the fuel may be sufficiently preconditioned to undergo spontaneous ignition without relying on a spark when it is mixed with air and compressed during the immediately following compression stroke. This type of combustion, called active radical combustion (ARC) by Honda, premixed charge compression ignition (PCCI) by Toyota or homogeneous charge compression ignition (HCCI) by Southwest Research Institute, is different from the conventional gasoline type spark ignition or diesel type compression ignition in that the whole cylinder charge ignites spontaneously and simultaneously, resulting in ultra-low NOx emissions.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.
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Ford Global Technologies Inc.
Hanze Carlos L.
Solis Erick
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