Fuel rails for supplying gasoline fuel to an internal combustion engine are well known in the art. These fuel rails generally provide a manifold from which fuel is distributed to a plurality of individual fuel injectors (i.e. "multi-point" fuel injection).
In the most common arrangement, fuel is pumped from a fuel reservoir, through a fuel supply line, to the fuel rail. In some designs, a fuel pressure damper is employed at a point upstream of the fuel rail. Fuel flows through the fuel rail to a plurality of fuel injectors. The fuel rail is attached to the top of the fuel injectors, and supplies fuel into the upper end of each fuel injector, which then injects the fuel into the intake manifold of the engine. Normally, not all of the fuel passing through the rail is fed to the injectors. The remaining fuel passes through the fuel rail to a fuel return line. Typically, a fuel pressure regulator is employed in the fuel return line downstream of the last injector. Fuel exhausted from the injectors is then returned to the reservoir via the return line.
International PCT Publication WO 92/08886 discloses another arrangement whereby two separate fuel rails are employed, one as a fuel inlet rail and the second as a fuel outlet rail. The fuel inlet rail branches to supply each fuel injector with fuel at a "bottom feed" location. The inlet rail is not directly in fluid communication with the fuel return line, as in the above-described arrangement. Instead, all of the fuel in the inlet rail is supplied to the injectors and uninjected fuel is passed through each injector, out its upper end, and to the fuel outlet rail. Fuel then passes from the outlet rail, through a regulator, and back to the reservoir via a fuel return line.
Prior art fuel rails are predominantly designed for use with gasoline or diesel fuels. However, little has been done in the art with respect to fuel rails for supplying liquid petroleum gas ("LPG") to an internal combustion engine.
Interest in alternative fuels, such as LPG, has increased in recent years due to the inherent cost and environmental advantages over other fuels. LPG has particularly received much attention as an alternative to gasoline or diesel for use in internal combustion engines. Propane, the primary constituent of LPG, is a byproduct of the refining of gasoline, and it is a byproduct of the transfer of natural gases in pipelines. It is readily available and at costs far below that of gasoline.
LPG was recently listed under the Clean Air Act in the United States as a suggested alternative fuel because it is more environmentally compatible than gasoline. LPG burns more completely, producing less carbon monoxide and hydrocarbon emissions. Also, using LPG as a fuel reduces the emission of volatile organic compounds which occurs during gasoline refueling.
The United States Federal Government recently promulgated legislation, referred to as Corporate Average Fuel Efficiency ("CAFE") standards, to promote the use of more environmentally compatible fuels. CAFE created a system of incentives which encourages manufacturers to build automobiles and trucks which use alternative fuels such as LPG. As a result, there is increased interest in manufacturing and retrofitting automobiles and trucks to be fueled with LPG.
The injection of liquid fuels such as gasoline into internal combustion engines is well known (see U.S. Pat. No. 4,700,891). Such fuel injectors create fine atomization of liquid fuel, which improves the efficiency of the burning cycle.
Although LPG in its gaseous form has been used as a reasonably effective fuel in internal combustion engines, there is an associated reduction in power capability as compared to liquid LPG fuels. This power reduction is mainly due to the reduced amount of air and fuel which can be drawn into the intake manifold when the LPG enters the manifold in gaseous form.
With liquid LPG, a further gain in power (and simultaneous reduction in the emission of nitrous oxides) results from the cooling of air and fuel within the manifold from vaporization of injected LPG. This also reduces the tendency for engine knock.
Use of LPG in liquid form as a fuel is fairly new in the art. However, several obstacles are associated with attempting to inject liquid LPG directly into the intake manifold of an internal combustion engine. In particular, it is difficult to maintain LPG in its liquid state near the heated engine compartment. LPG has a very low boiling point (See FIG. 6 for the liquid-vapor phase boundaries for propane and isobutane, the primary constituents of LPG). Even under pressure, LPG will tend to bubble or boil as the boiling temperature at a given pressure is approached. The formation of bubbles, often called "champagning" or "flashing," can cause inconsistent injection and poor air/fuel ratio control.
It is thus very desirable to cool supply LPG to prevent the bubbling or boiling which can occur when attempting to inject a low boiling point fuel in a fully liquid state. Although other approaches to cooling LPG have been attempted (see, e.g., U.S. Pat. No. 4,489,700 and U.S. Pat. No. 5,076,244), none have addressed the cooling problem in the design of the fuel rail itself.
Another significant problem encountered with using LPG as a fuel is the contaminants which are contained therein. These contaminants collect in fuel lines, injectors and regulators and can hinder performance. Thus, it would be beneficial if the fuel rail was designed to aid in the removal of these contaminants.
Consequently, it is clear that a simple and effective fuel rail which aids in cooling LPG to maintain it in a liquid state and which promotes the removal of fuel contaminants has been needed.