Internal-combustion engines – Charge forming device – Gaseous fuel and air mixer
Reexamination Certificate
1998-02-12
2001-02-20
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Gaseous fuel and air mixer
C123S525000
Reexamination Certificate
active
06189517
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to internal combustion engines, such as used in vehicles, and more particularly direct injected compression-ignition (CI) engines using clean low viscosity fuels such as dimethyl ether (DME) to achieve ultra-low emissions of oxides of nitrogen and particulate matter.
The background of air pollution problems caused especially by internal combustion engines in trucks and buses as well as proposed solutions to such problems are set forth in detail in my U.S. Pat. No. 5,816,228, entitled FUEL INJECTION SYSTEM FOR CLEAN LOW VISCOSITY FUELS, the disclosure of which is incorporated herein by reference. One promising solution involves the use of DME as an alternative fuel for CI engines. However, conventional fuel systems are not suitable for use with DME because of the low viscosity of such a fuel. As disclosed in U.S. Pat. No. 5,816,228, a pressurized fuel storage tank is required, as well as a special pressurized fuel injection system.
A major problem with using DME is internal leakage of DME within the fuel injection system of a CI engine. In the fuel injection system as disclosed in U.S. Pat No. 5,816,228, DME is supplied under pressure to an accumulator, also called a common rail, and then is fed through a solenoid operated control valve to a fuel injector. When the engine is shut down, fuel can leak from the accumulator to the fuel injectors since the control valves are of the spool type. The fuel injector nozzle valves are precision steel valves, but they form imperfect seals for DME. Accordingly, when the engine is shut down, fuel can also pass through the fuel injector nozzle valves over a period of time and enter the associated combustion cylinders of the engine which is not acceptable. Accordingly, leakage from the accumulator to the fuel injectors must be prevented.
Even if means is provided for effectively preventing DME from leaking from the accumulator into the fuel injectors after the engine is shut down, a small volume of fuel will be trapped in the injectors upon engine shut down which could eventually leak into the combustion chambers of the engine. This type of leakage must also be prevented.
SUMMARY OF THE INVENTION
The invention incorporates a novel fuel tank which utilizes a fuel such as DME as the fuel to be pumped, and a second fluid such as propane as a pumping medium. The vapor pressure of the propane is higher than the vapor pressure of the DME to thereby cause the DME to be under substantially constant pressure by the propane at any particular ambient temperature over a wide range of ambient temperatures. This arrangement ensures that the DME will be maintained in its liquid phase. The fuel injection system of the present invention is similar to that shown in U.S. Pat. No. 5,816,228 except that a leakage control system is provided in the present invention for solving the leakage problems occurring with the system shown in said application.
In the present invention, the leakage control system includes a novel check valve for preventing fuel from leaking from the accumulator to any fuel injector when the engine is shut down and the pressure of the liquid fuel in the accumulator drops below a predetermined level. This check valve utilizes a soft, high strength ball which conforms to the valve seat of the check valve and provides a pressure-tight seal. The ball is urged toward its closed position by a piston which engages the ball. The piston is biased by resilient means in the form of a spring in a direction to cause the ball to engage the valve seat. The ball has a diameter and the piston has a face which is circular and has a diameter greater than the diameter of the ball.
The construction of the check valve is such that it has a very high opening pressure and a relatively low closing pressure. When the check valve is seated, the fuel pressure acts on a relatively small area of the ball, and when the ball initially lifts off of the seat, the fuel will act on the end of the piston which causes the total area acted on by fuel to be suddenly increased thereby causing the check valve to open rapidly to its full open position.
The check valve is always in its wide open position when the engine is running; and the only time the valve closes is when the engine is shut down. Therefore, the check valve has only very limited mechanical cycles of about 30,000 cycles between engine overhauls, so that the valve should last indefinitely.
The leakage control system of the invention also includes means for handling the small amount of fuel trapped in the fuel injectors when the engine is shut down. An adsorber means comprises a container filled with a material such as activated charcoal, the container having an inlet and an outlet. When the engine is shut down and the check valves have closed, the fuel injectors are connected to the inlet of the container, and the outlet of the container is simultaneously connected to the air inlet of the engine. Fuel vapors trapped in the fuel injectors then flow into the container and are adsorbed by the charcoal.
When the engine is restarted, the fuel injectors are disconnected from the inlet to the container and the outlet of the container is simultaneously disconnected from the air inlet of the engine. After a time delay when the associated vehicle is not moving, the inlet of the adsorbing means is connected to a source of purge air, and the outlet of the adsorbing means is simultaneously connected to the air inlet of the engine. The purge air flows into the container and purges the adsorbed fuel vapors which flow into the engine air inlet where they are burned. This purge process continues for a short period of about two to five minutes whereupon the source of purge air and the engine air inlet are simultaneously disconnected from the adsorber means.
The leakage control system then remains inactive while the engine is running until the engine shuts down again, whereupon the leakage control system recycles through the sequence of steps described above.
Thus, the leakage control system effectively overcomes the leakage problems in a DME fueled IC engine.
REFERENCES:
patent: 3651794 (1972-03-01), Douglas
patent: 3698367 (1972-10-01), Goodwin
patent: 4721078 (1988-01-01), Watanabe et al.
patent: 5421161 (1995-06-01), Gustafson
patent: 5509393 (1996-04-01), Leaf et al.
patent: 5690078 (1997-11-01), Ofner
patent: 5755210 (1998-05-01), Sato et al.
AVL Powertrain Engineering, Inc.
Moulis Thomas N.
Watson Cole Grindle Watson, P.L.L.C.
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