Method and System for Controlling Emission from an Off-Road Engine

Abstract

In a method and system for controlling emission from a four-stroke off-road engine that 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, and the method 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.

1 . A method for controlling emission from a four-stroke off-road engine, the off-road engine being 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 being provided with an oxidation catalyst for converting hydrocarbon and carbon monoxide, the method comprising:
 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.   
   
   
       2 . The method of  claim 1 , wherein injection of fresh air into the exhaust gas discharging assembly is conducted using a one-way valve which is connected to the exhaust gas discharging assembly at the upstream side of the oxidation catalyst and which is operable in such a manner that the one-way valve is opened during a suction stroke of the off-road engine and is closed during a compression stroke of the off-road engine, thereby permitting intermittent injection of fresh air into the exhaust gas discharging assembly. 
   
   
       3 . The method of  claim 1 , wherein injection of fresh air into the exhaust gas discharging assembly is conducted using a one-way fan which is connected to the exhaust gas discharging assembly at the upstream side of the oxidation catalyst and which is operable in such a manner that the one-way fan is driven to rotate during a suction stroke of the off-road engine and is stopped from rotating during a compression stroke of the off-road engine, thereby permitting intermittent injection of fresh air into the exhaust gas discharging assembly. 
   
   
       4 . The method of  claim 1 , wherein the ratio of air to fuel of the fuel rich fuel-and-air mixture is adjusted using a carburetor which is disposed at an upstream side of the off-road engine. 
   
   
       5 . The method of  claim 1 , wherein the oxidation catalyst is installed in a muffler of the exhaust gas discharging assembly, and the fresh air is injected into the muffler. 
   
   
       6 . An emission control system for controlling emission from an off-road engine, comprising:
 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 said muffler for injecting intermittently fresh air into said muffler at an upstream side of said oxidation catalyst by virtue of suction and compression strokes of the off-road engine.   
   
   
       7 . The emission control system of  claim 6 , wherein said air injection member includes a one-way valve connected to said muffler. 
   
   
       8 . The emission control system of  claim 6 , wherein said air injection member includes a one-way fan connected to said muffler.