Fluid sprinkling – spraying – and diffusing – Combining of separately supplied fluids – And valving means controlling flow for combining
Reexamination Certificate
2000-04-18
2002-01-08
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Combining of separately supplied fluids
And valving means controlling flow for combining
C409S061000
Reexamination Certificate
active
06336598
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel hydraulically actuated dual fuel injector for an internal combustion engine. More particularly, the application pertains to a hydraulically actuated injector for injecting controlled quantities of a first fuel and a second fuel into an internal combustion diesel engine at different times.
BACKGROUND OF THE INVENTION
Because of its ready availability, low cost and potential for reducing particulate emissions, natural gas is a promising candidate for fuelling diesel engines. Known methods for converting a conventional diesel-fuelled engine (that is, a compression-ignition engine) to consume natural gas fall into three general approaches:
(1) Converting the engine to a stoichiometric or lean-burn spark-ignition engine;
(2) Converting the engine to natural gas using a “dual-fuel” technology, in which the natural gas is mixed with all of or with a portion of the intake air and is ignited by diesel fuel injected at the end of the compression stroke; and
(3) Converting the engine to directly inject the natural gas fuel into the combustion chamber, with a source of ignition.
The differences between these three approaches are elaborated upon in the more detailed discussions of these methods in the following paragraphs. However, the preferred method, is the direct injection method because it is the only method that preserves the inherent favorable operating characteristics and high efficiency of conventional diesel-fuelled engines.
(1) Fuelling Diesel Engines with Premixed Air and Natural Gas—Spark Ignition
A conventional diesel-fuelled engine can be converted to natural gas by injecting natural gas with the intake air and allowing the mixture to enter the chamber through the intake valve. The mixture, stoichiometric or lean, can then be ignited near top dead center using spark plugs. However, to avoid detonation of the mixture, the compression ratio of the engine must be reduced. A reduction in compression ratio is accompanied by a reduction in efficiency, or equivalently by an increase in fuel consumption. Furthermore, to maintain the strength of the mixture under all conditions, the intake air must be throttled, causing pumping losses and further increasing the fuel consumption required to maintain equivalent power. These losses are especially pronounced at low or part load levels, which are the predominant operating conditions of automotive engines. Typically, the conversion of diesel engines to stoichiometric or lean-burn combustion of natural gas with spark plug ignition offers a considerable reduction in harmful emissions, but also leads to an increase in fuel consumption.
(2) Fuelling Diesel Engines with Premixed Air and Natural Gas Pilot Injection
In this method, the natural gas is generally admitted in the intake air and enters the combustion chamber through the intake ports or valve. The mixture is ignited near top dead center by the injection of pilot diesel fuel. There are, however, fundamental complications with this method:
1. At low load, with unthrottled diesel operation, the gas fuel and air mixture is too lean for satisfactory combustion. The fuel consumption increases under these conditions and the hydrocarbon emissions also increase. Remedies to this situation include:
a. Reverting to diesel fuel operation at low loads—in some applications where substantial part load conditions exist this remedy defies the purpose of the fuel substitution.
b. Throttling of the intake air, which is complicated when the engine is equipped with turbochargers because of the danger of compressor surge (although with modern electronic-controlled waste gates this may be avoidable). In any case, such throttling removes an inherent advantage of diesel operation.
c. Skip-firing, which consists of not firing the cylinders at each cycle but rather at every other cycle. This method does not usually permit smooth engine operation, particularly on 4 cylinder engines, and is usually too unstable for idling, requiring straight diesel operation.
2. Because a premixed fuel-air mixture exists during the compression, there is a danger of knocking (an uncontrolled combustion of the mixture), with potential engine damage. Thus, reduction in compression ratio may be required. If a reduction in compression ratio is chosen, the engine efficiency is compromised. If the compression ratio is maintained, the amount of natural gas used under each condition must be limited such that the mixture formed is not prone to knocking. This means that more diesel fuel must be used to sustain high load cases.
This pilot ignition method and the previously discussed spark ignition method are not well suited for 2-stroke engines because a substantial amount of the intake charge flows out the exhaust valve in two-cycle engines and is wasted. To avoid this bypass, and to improve on the low load combustion characteristics, it has been proposed to inject the natural gas directly into the combustion chamber after all valves or ports are closed, but still at a relatively low pressure. This adds difficulty because a new injection system control is needed, modifications to the head or block are required, and metering the gaseous fuel and ensuring stratification is difficult.
So far as is known, this second method has been proven capable of maintaining the efficiency over a wide range of load and speeds only by retaining a substantial amount of diesel fuel to compensate for the above problems.
(3) Direct Injection of Natural Gas into Diesel Engine Cylinders
The great advantage of directly injecting fuel into the engine cylinders in diesel operation is that it permits efficient and stable burning over the whole load range. This is because the burning occurs in local regions in which the fuel-air ratio is within the prescribed flammability limits. When a gaseous fuel such as natural gas is substituted for diesel fuel, the gaseous fuel has an advantage over diesel fuel in that it does not require atomization into micron-sized droplets and thus does not require very high injection pressures. For diesel injection, pressures as high as 1000 atmospheres are required for most efficient operation. For a gaseous fuel such as natural gas, pressures of 200 atmospheres are satisfactory. The principal difficulty with the direct injection of natural gas is that natural gas will not self-ignite, as diesel fuel does, at the typical temperature and pressure range of a diesel engine. To overcome this difficulty, another source of ignition must be provided. Examples of ignition sources are: (a) a small quantity of self-igniting pilot diesel fuel injected with or separate from the natural gas, and (b) glow plugs or hot surfaces and the like. For economic reasons, it is desirable to limit the necessary modifications to the engine. In that respect, an advantageous design employs a dual-fuel injector that fits in the same opening as a conventional single-fuel injector so that both a pilot fuel and a gaseous fuel can be injected into the combustion chamber without modifying the engine block or cylinder head.
Successful operation of large bore diesels with direct injection of compressed natural gas has been demonstrated in North America, as discussed in the following publications:
1. J. F. Wakenell, G. B. O'Neal, and Q. A. Baker, “High Pressure Late Cycle Direct Injection of Natural Gas in a Rail Medium Speed Diesel Engine”, SAE Technical Paper 872041;
2. Willi, M. L., Richards, B. G., “Design and Development of a Direct Injected, Glow Plug Ignition Assisted, Natural Gas Engine”, ICE—Vol. 22, Heavy Duty Engines: A look at the Future, ASME 1994; and
3. Meyers. D. P., Bourn, G. D., Hedrick, J. C., Kubesh, J. T., “Evaluation of Six Natural Gas Systems for LNG Locomotive Applications”, SAE Technical Paper 972967.
Meyers et al. at the Southwest Research Institute demonstrated the superiority of the direct injection of natural gas over other means of fuelling a locomotive engine with natural gas. The direct injection of natural gas led to the best thermal efficiency for the targeted reduction of ni
Baker S. Michael
Benson Donald J.
Douville Bradley D.
Ghuman A. S.
Perr Julius
Hwu Davis
McAndrews Held & Malloy Ltd.
Scherbel David A.
Westport Research Inc.
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