Patent Description:
Water injection is a proven technique for raising the threshold at which detonation (or pre-ignition) takes place in an internal combustion engine (ICE). An increased pre-ignition threshold enables the use of lower octane and/or cetane fuels in tandem with higher compression ratios for higher power output and increased operating range. <CIT> discloses a water injection system.

The invention provides an air compression system including an internal combustion engine and an air compressor driven by the internal combustion engine. The air compressor is operable to draw in atmospheric air and discharge a mixed flow of compressed air and water. The air compression system further includes a water injection system for supplying water into the internal combustion engine, a separator assembly in communication with the air compressor that separates the water from the compressed air, and a water passageway interconnecting the separator assembly and the water injection system. The air compressor supplies a supply of water to the water injection system.

In another embodiment the invention provides a method of operating an air compressor. The method includes compressing ambient air using an air compressor to convert the ambient air to compressed air and water, operating an internal combustion engine to power the air compressor, separating the water from the compressed air exiting the air compressor in a separating assembly, collecting the water from the separating assembly, and feeding a portion of the collected water to the internal combustion engine with a water injection system.

In another embodiment the invention provides an air compression system including an air compressor operable to draw in ambient air and compress that air to produce a flow of compressed air and water. The air compression system further includes an engine coupled to the air compressor. The engine is operable in response to the combustion of a flow of fuel to power the air compressor. The air compression system further includes a moisture separator coupled to the air compressor and arranged to receive the flow of compressed air and water. The moisture separator is operable to separate a portion of the water from the flow of compressed air and water and to discharge a flow of compressed dry air and a flow of liquid water. The air compression system further includes a reservoir positioned to receive the flow of liquid water and a water injection system coupled to the engine. The water injection system is operable to draw water from the reservoir and inject that water into the engine for combustion. The air compression system further includes a controller operable to vary the quantity of water delivered to the engine.

<FIG> illustrates an air compressor system <NUM> including an air compressor <NUM>, an internal combustion engine (i.e., ICE) <NUM> for providing work to drive the air compressor <NUM>, and a water injection system <NUM> that provides water to the ICE <NUM>. As those of skill in the art will understand, all air contains some water vapor. As the air is compressed, the dew point (i.e., the temperature at which condensation occurs), as well as the temperature of the air rises. Typically, the temperature remains above the dew point within a compressor so that condensation does not occur. However, to meet customer expectations for compressed air approach temperatures, and implicitly compressed air moisture levels, an air-air heat exchanger or aftercooler <NUM> is often integrated into the compressed air discharge lines downstream of a separator tank <NUM> to reduce the compressed air discharge temperature. Typically, this temperature reduction is accompanied by water condensation as the resultant temperatures are below the dew point for the system in question and common ambient conditions. In some constructions a filter <NUM> is positioned downstream of the aftercooler <NUM> to remove the additional condensate. Thus, an air compressor typically draws in atmospheric air (which includes water vapor) and discharges a flow of compressed air and water, wherein the water is in the form of liquid water and/or water vapor.

To separate this condensate, the system <NUM> also incorporates a moisture separator assembly <NUM> having the aftercooler <NUM>, the separator tank <NUM>, and a filter <NUM>. The filter <NUM> filters the compressed air downstream of the aftercooler <NUM> and in many constructions is omitted. Generally speaking, the separator assembly <NUM> receives compressed air from the air compressor <NUM>. The separator tank <NUM> may include, for example, a centrifugal or cyclonic separator which operates in a conventional manner. For example, the separator tank <NUM> may be arranged to admit the compressed air from the compressor <NUM> in a substantially tangential direction. As the air moves in a cyclonic pattern, heavier water particles are forced outward until they impact the surface of the separator tank <NUM> and drain to the bottom of the separator tank <NUM>. In other constructions, flow obstructions, walls, or baffles may be positioned to force changes in the air flow direction which aid in separating the heavier water particles.

With reference to <FIG>, the separator assembly <NUM> includes a first or "air outlet" <NUM> for allowing air to exit the separator assembly <NUM> and a second or "liquid outlet" <NUM> for allowing liquid to exit the separator assembly <NUM>. The air outlet <NUM> is coupled to an air passageway <NUM> and may be in communication with a filter <NUM> to further remove hydrocarbon content from the compressed air stream. The liquid outlet <NUM> is coupled to a liquid passageway <NUM> and is in communication with the water injection system <NUM>. The liquid passageway <NUM> may include a valve <NUM> that is operable to redirect or discharge liquid passing through the liquid passageway <NUM> when there is an excess of liquid from the separator assembly <NUM>.

With continued reference to <FIG>, the water injection system <NUM> includes a reservoir <NUM> that provides water to a pump <NUM> which, in turn, provides water via a fluid conduit <NUM> to a water injector unit <NUM>. The water injector unit <NUM> is coupled to and in communication with the ICE <NUM> to provide direct water injection to the ICE <NUM>. For example, the water injector unit <NUM> may inject water into the ICE <NUM> at each compression cycle or some other various timing pattern. Upstream of the water injector unit <NUM> is a valve or a control system <NUM> that regulates the amount or time at which water is directed to the water injector unit <NUM>. The location at which water is injected into the ICE <NUM> is not critical. Therefore, water could be injected into an air stream <NUM>, a fuel stream <NUM>, a mixed fuel air stream <NUM>, or directly into an engine piston-cylinder <NUM> as may be desired.

In operation, the internal combustion engine <NUM> is powered through a typical fuel-combustion process. In this case, the ICE <NUM> provides work into the air compressor <NUM> to drive the compressor <NUM>. As the air compressor <NUM> is driven by the ICE <NUM>, air enters the air compressor <NUM> at an ambient pressure and exits the air compressor at a higher pressure based in part on the compression ratio of the compressor <NUM>. From there, the separator assembly <NUM> receives the compressed air. As noted above, the compressed air can cool to a temperature below the dew point of the compressed air, thereby allowing for condensation in the compressed air. The separator assembly <NUM> separates the liquid water from the compressed air. The liquid water is directed toward the liquid outlet <NUM> and passed through the liquid passageway <NUM>. Simultaneously, the compressed air within the separator assembly <NUM> is directed toward the air outlet <NUM>, passes through the air passageway <NUM> and the filter <NUM>, and exits the system <NUM> as compressed air where it can be used as desired.

With reference to <FIG>, the piston-cylinder <NUM> of the ICE <NUM> is in communication with the reservoir <NUM> of the water injection system <NUM>. The piston-cylinder <NUM> is a conventional piston-cylinder arrangement having a piston <NUM> that reciprocates within a cylinder <NUM>. While a common piston-cylinder arrangement <NUM> is illustrated in <FIG>, the ICE <NUM> could include a rotary engine, could be a diesel engine, and could include more than one piston-cylinder as required by the particular construction.

When water is desired, the water, air, and fuel are mixed in the cylinder <NUM> to facilitate the desired combustion process, or prior to entry into the cylinder <NUM> for combustion. The water adds mass and therefore power to the ICE <NUM>. The water assists in cooling the engine and lowers the temperature of the combustion and compression cycle. The illustrated ICE <NUM> includes a spark plug <NUM> or similar igniter for igniting the fuel (e.g., gasoline, petrol, alcohol, natural gas, etc.). In other embodiments, the ICE <NUM> may alternatively employ compression ignition like that used in diesel powered engines, with or without the addition of the igniter <NUM>. Once the fuel has ignited during the compression cycle, the exhaust is discharged out to ambient surroundings.

In one operating mode, a controller (e.g., the valve or control system <NUM>) monitors the engine load for controlling when and how much water is injected into the ICE <NUM>. Specifically, the ICE <NUM> includes a demand sensor <NUM> positioned to measure a value indicative of the power output of the ICE <NUM> by measuring a compressed air flow rate. The controller <NUM> receives a signal from the demand sensor <NUM> indicative of the measured flow rate, and the controller <NUM> varies a power level of the ICE <NUM> at least partially in response to the measured flow rate. Also, the controller <NUM> varies the quantity of water delivered to the ICE <NUM> at least partially in response to the measured flow rate. For example, when the engine load exceeds a predetermined value, the water injection system <NUM> is activated to provide water, and therefore extra power, to the ICE <NUM>. When water is called for, the valve <NUM> is opened at the proper time intervals to inject the proper quantity of water into the piston-cylinder <NUM>.

The water injection system <NUM> is advantageous as it uses water that is produced naturally as a by-product of the air compression and cooling processes of the air compressor <NUM>. Typically viewed as a waste, the water produced from the air compressor <NUM> is collected in the reservoir <NUM> and used by the water injection system <NUM>. Typically, water injection systems for use with mobile applications are difficult to implement due to a lack of maintenance-free, continuous source of water. However, the ICE <NUM> and the water injection system <NUM> have a maintenance-free, continuous source of water via the air compressor <NUM>.

In addition, the use of water injection can increase the maximum power output of the engine <NUM> such that it might be possible to use a smaller engine than what might be required without water injection. For example, the engine <NUM> could be sized to provide <NUM> percent of the maximum expected power requirements with water injection providing the extra <NUM> percent when required.

Claim 1:
An air compressor system (<NUM>) comprising:
an internal combustion engine (<NUM>) operable to produce a power output in response to combustion of a fuel-air mixture;
an air compressor (<NUM>) driven by the internal combustion engine (<NUM>) and operable to draw in atmospheric air and discharge a mixed flow of compressed air and water;
a separator assembly (<NUM>) in communication with the air compressor (<NUM>) and operable to separate the mixed flow of compressed air and water into a flow of compressed air and a separate flow of water;
a water injection system (<NUM>) for supplying the flow of water to the fuel-air mixture and into the internal combustion engine (<NUM>);
a water passageway (<NUM>) interconnecting the separator assembly (<NUM>) and the water injection system (<NUM>), the water passageway (<NUM>) configured to direct the flow of water to the water injection system (<NUM>);
an air passageway (<NUM>) fluidly connected to the separator assembly (<NUM>), wherein the compressed air is discharged from the separator assembly (<NUM>) through the air passageway (<NUM>), and exits the air compressor system (<NUM>);
a sensor (<NUM>) configured to detect a flow rate of compressed air through the air passageway (<NUM>); and
a control system coupled to the internal combustion engine (<NUM>) and the water injection system (<NUM>), the control system configured to regulate an amount of water supplied to the internal combustion engine (<NUM>) in response to the detected flow rate of compressed air by the sensor (<NUM>).