Patent Application
20080282672
1. Field of the Invention
This invention relates to a method and an emission control system for controlling emission from an off-road engine, more particularly to a method and an emission control system involving injecting a fuel rich fuel-and-air mixture into an off-road engine and fresh air into an exhaust gas discharging assembly for controlling emission from the off-road engine.
2. Description of the Related Art
In order to meet emission standards, such as CARB III and EPA III, which will be applicable to many states of the United States in the near future, conventional gasoline off-road engines, particularly for four-stroke engines with a power output of less than 30KW, normally incorporate electronic fuel injection (EFI) means therein for adjusting an optimum air/fuel ratio of a fuel-and-air mixture to be injected into the off-road engine. However, this approach is relatively expensive and is not economically suitable for application to the off-road engine with a carburetor. In addition, conventional off-road engines normally produce a high concentration of NO, in the exhaust gas and thus require installation of a reduction catalyst (Rh), which is used to reduce NO, in the exhaust gas, in addition to an oxidation catalyst (Pt/Pd), which is used for converting hydrocarbon and carbon monoxide in the exhaust gas into water and carbon dioxide.
Therefore, the object of the present invention is to provide a method and an emission control system that can overcome the aforesaid drawbacks of the prior art.
According to one aspect this invention, there is provided a method for controlling emission from an off-road engine. The off-road engine is provided with an exhaust gas discharging assembly at a downstream side thereof for discharging of the exhaust gas from the off-road engine. The exhaust gas discharging assembly is provided with an oxidation catalyst for converting hydrocarbon and carbon monoxide. The method comprises injecting a fuel rich fuel-and-air mixture into the off-road engine, and injecting fresh air into the exhaust gas discharging assembly at an upstream side of the oxidation catalyst.
According to another aspect this invention, there is provided an emission control system for controlling emission from a four-stroke off-road engine. The emission control system comprises: a carburetor adjusted to an operating state so as to be capable of providing a fuel rich fuel-and-air mixture to be injected into the off-road engine; a muffler adapted to be connected to the off-road engine and provided with an oxidation catalyst therein for converting hydrocarbon and carbon monoxide in exhaust gas from the off-road engine; and an air injection member connected to the muffler for injecting intermittently fresh air into the muffler at an upstream side of the oxidation catalyst by virtue of suction and compression strokes of the off-road engine.
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:
Before the present invention is described in greater detail with reference to the accompanying preferred embodiments, it should be noted herein that like elements are denoted by the same reference numerals throughout the disclosure.
The present invention relates to a method and an emission control system for controlling emission from a gasoline off-road engine, particularly from a four-stroke engine with a power output of less than 30KW. The off-road engine is provided with an exhaust gas discharging assembly at a downstream side thereof for discharging of the exhaust gas from the off-road engine. The exhaust gas discharging assembly is provided with an oxidation catalyst for converting hydrocarbon and carbon monoxide into water and carbon dioxide. In order to achieve the emission control, the method of this invention includes the steps of injecting a fuel rich fuel-and-air mixture into the off-road engine, and injecting fresh air into the exhaust gas discharging assembly at an upstream side of the oxidation catalyst so as to provide sufficient oxygen for reaction with hydrocarbon and carbon monoxide in the exhaust gas upon passing through the oxidation catalyst.
The emission control system includes: a carburetor 10 operable to blend an air stream 101 and a fuel stream 102 and adjusted to an operating state so as to be capable of providing a fuel rich fuel-and-air mixture 103 to be injected into the off-road engine 20; a muffler 30 of the exhaust gas discharging assembly connected to the off-road engine 20 and provided with an oxidation catalyst 40 therein for converting hydrocarbon and carbon monoxide in an exhaust gas stream 104 from the off-road engine 20; and an air injection member 50 connected to the muffler 30 for injecting intermittently fresh air 105 into the muffler 30 at an upstream side of the oxidation catalyst 40, which is installed in a middle of the muffler 30, by virtue of suction and compression strokes of the off-road engine 20. The discharged exhaust gas 106 thus treated from the muffler 30 can meet the emission standards, such as CARB III and EPA III, set in the United States.
In this embodiment, the air injection member 50 for injecting fresh air 105 into the muffler 30 of the exhaust gas discharging assembly includes a reed-type one-way valve 501 (see
The emission control system of this invention is advantageous in that under a fuel rich condition, the concentration of generated NO, in the exhaust gas is considerably reduced, which permits omission of the reduction catalyst as required in the prior art. Although the concentration of the hydrocarbon and carbon monoxide in the exhaust gas is increased as a result of operating under a fuel rich condition, the injection of fresh air into the muffler 30 is capable of reducing the concentration of the hydrocarbon and carbon monoxide to an extent to meet the aforesaid emission standards.
Table 1 shows the results of emission analysis for the off-road engine 20 incorporated with or without the air injection member 50 of this invention and for different catalyst combinations, which are respectively Examples 1 to 3 (represented by E. 1 to 3) and Comparative Examples 1 to 3 (represented by CE. 1 to 3).
The results show that with the inclusion of the air injection member 50 in the emission control system of this invention, i.e., with the inclusion of injecting fresh air into the exhaust gas discharging assembly according to the method of this invention, the concentration of hydrocarbon and carbon monoxide in the exhaust gas can be reduced significantly as compared to that without the air injection member 50 or injection of fresh air into the muffler 30. In addition, the cost of incorporating the air injection member 50 into the exhaust gas discharging assembly is much cheaper than that of incorporating with the EFI means.
While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements.
