This invention relates to heating charge air and the mixing of air, fuel and water using Venturi to deliver a temperature controlled charge to a Homogeneous Charge Compression Ignition (HCCI) engine. The well-mixed charge provides the homogeneous mixture necessary for compression ignition and mitigates an inherent problem of fuel stratification on internal surfaces. Fuel could be gasoline but could also be natural gas, other hydrocarbons, alcohols, or diesel. The invention recovers heat energy from the exhaust and improves combustion due to enhanced mixing, resulting in improved combustion and fuel economy.
Homogeneous Charge Compression Ignition (HCCI) engines operate by auto-igniting a heated fuel/air mixture by engine compression. The advantage of a HCCI engine includes low NOx emission resulting from the short combustion time and greater engine efficiency than a spark ignited engine. Challenges to HCCI engine design include unburned hydrocarbon emissions caused by fuel stratification on internal engine surfaces and auto-ignition timing.
Of the six pollutants (carbon monoxide, lead, nitrogen oxides, particulate matter, sulfur dioxide, and volatile organic compounds) tracked by the Environmental Protection Agency, all have decreased significantly since passage of the Clean Air Act in 1970—except for nitrogen oxides
Air is composed of 78 volume percent nitrogen. Nitrogen oxidizes when fuel is burned at high temperatures, as in a combustion process to form nitrogen oxides. Nitrogen oxides consist of a group of oxidized nitrogen compounds collectively known as NOx. Many of the nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide (NO2) along with particles in the air can often be seen as a reddish-brown layer over many urban areas. The primary source of NOx is motor vehicles. Production of NOx increases with the time and temperature of combustion.
The differential producing Venturi has a long history of uses in many applications. With no abrupt flow restrictions, the Venturi can mix gases and liquids with a minimal total pressure loss. Recently, the Venturi has been used in carbureted engines. The suction from the throat of the Venturi provided the motive force for bringing the fuel in contact with the air. The improved application of the Venturi with the proposed invention is: the metering of the fuel is controlled by the fuel injector instead of the suction of the venturi; the fuel vaporization is facilitated by the reduced pressure in the throat of the Venturi; and mixing of the fuel/air mixture is further facilitated by the turbulent action in the outlet of the Venturi.
The principle behind the operation of the Venturi is the Bernoulli effect. The Venturi mixes vapors and liquids by reducing the cross sectional flow area in the air flow path, resulting in a pressure reduction in the throat of the Venturi. After the pressure reduction, the mixture is passed through a pressure recovery exit section where most of the pressure reduction is recovered. The pressure differential follows Bernoulli's Equation, simplified for a negligible change in elevation:
P1+1/2d1v12=P2+1/2d2v22
where,
P1=Pressure at the inlet of Venturi (
P2=Pressure at the throat of the Venturi (
d1=air density at the inlet of the Venturi (
d2=air density at the throat of the Venturi (
v1=air velocity at the inlet of the Venturi (
v2=air velocity at the throat of the Venturi (
In
This disclosure offers solutions to the two main challenges of HCCI engines: 1) timing of the auto-ignition and 2) residual hydrocarbon emissions resulting from fuel stratification on internal surfaces of the combustion chamber.
Auto-ignition timing is accomplished by controlling the mixture charge temperature with a water injection stream. Specifically, water is injected into the throat of the Venturi where homogeneous mixing is accomplished with fuel and air. Air is defined for the purposes of this disclosure as a vapor containing oxygen. Water is defined as liquid containing water, recognizing that anti-freeze components may be required for cold weather operation. The mixture temperature is lowered because of the low water temperature relative to the hot air charge and because of the latent heat of evaporation of the water. The temperature of the homogeneous charge then changes the ignition timing during the compression stroke. The water injection rate is controlled by the engine controls similar to the control of the spark in a conventional stratified charge engine. By changing the temperature of the charge mixture, auto-ignition timing can be controlled.
Residual fuel combusted on internal surfaces of the combustion chamber is mitigated by pre-mixing fuel and air immediately before delivering the mixed charge to the combustion chamber. A Venturi regulated by a pintle valve provides a high velocity at the mixing point regardless of the throttle position. For example, when a car is cruising down the highway at low throttle, the pintle is relatively closed into the throat of the Venturi. Consequently, the mixing velocity is much higher and mixing is more complete relative to an unregulated Venturi or a common butterfly throttle valve induction system.
Engine efficiency is improved by exchanging heat from the exhaust with charge air. Excess heat is absorbed by the latent heat of evaporation of water fed into the engine. Exhaust heat is therefore recovered by the phase change of water from the liquid phase in the Venturi feed to the vapor phase out the engine exhaust.
The vaporization of the fuel is improved in the Venturi throat by the heat transfer from the hot charge air. Gasoline is typically only 68% vaporized at 70 degrees Fahrenheit. A typical exhaust manifold temperature is about 450 degrees Fahrenheit. Consequently, there is sufficient heat available to substantially raise the fuel/air mixture temperature. The pre-heated air and Venturi mixing concept complement one another, resulting in better fuel/air pre-mixing because of the reduced pressure and increased turbulence at the throat of the Venturi. The result is improved fuel economy and engine performance.
Water is injected into the combustion chamber via the Venturi through injector 303 and the pintle openings 304 as required by the engine controls for auto-ignition timing. Although
With the regulated Venturi design, the fuel becomes well mixed with the air because: 1) the reduction in pressure at the throat of the Venturi increases the partial pressure of the fuel and promotes vaporization of the fuel and; 2) turbulence through the Venturi facilitates fuel/air mixing before the combustion chamber.
The pintle regulated Venturi design promotes enhanced fuel/air mixing at all throttle air rates by incorporating the air flow control with the Venturi design. The resulting flow area reduction provides a higher velocity at low throttle than an unregulated Venturi design. Consequently, the air velocity is always high into the throat of the Venturi, improving fuel/air mixing over the entire throttle range.