General-purpose engine with low exhaust gas emission

Abstract

The invention relates to a general-purpose engine with low exhaust gas emission, comprising a general-purpose engine case body, a cylinder head and a cylinder cover, wherein a cavity between the cylinder head and the cylinder cover is a rocker arm chamber; a muffler is communicated with an exhaust port of the cylinder head through an exhaust pipe; a crankcase cavity of the case body is communicated with the rocker arm chamber at the upper end of the cylinder head through an air duct; the cylinder cover is provided with an air inlet hole for communicating the outside with the rocker arm chamber; a one-way valve which is opened at negative pressure is arranged at the air inlet hole; and the cylinder cover is also provided with an air outlet which is communicated with the muffler through a one-way valve which is opened at positive pressure. Fresh air can be sucked into the rocker arm chamber for storage by the negative pressure formed in a crankcase when a piston of the engine reciprocates and the stored fresh air can be forced to be sent to the muffler by the positive pressure formed in the crankcase when the piston of the engine reciprocates, thus HC, CO and NOx in high-temperature exhaust gas exhausted from the engine can undergo fully chemical reaction with sufficient oxygen in the muffler and then can be exhausted, and the exhaust gas emission of the general-purpose engine can be effectively reduced.

Description

technical field [0001] The invention relates to the field of general engines, in particular to a general engine with low exhaust emission. Background technique [0002] The exhaust gas emitted by the engine contains a large amount of NOx, HC, CO and particulate matter, which pollutes the air extremely seriously. In order to reduce the air pollution caused by the exhaust gas emission of the engine, the current engine usually adopts a three-way catalyst in the exhaust muffler Carry out post-treatment, oxidize HC and CO, and reduce NOx, so as to reduce the content of HC, CO, and NOx in the exhaust gas; If the reduction is not sufficient, it is necessary to add air to the tail gas to increase the oxygen content in the tail gas, so as to promote the full oxidation or reduction of HC, CO, and NOx under the action of the three-way catalyst. However, the current method of reducing engine exhaust emissions is to use a negative pressure secondary air supply method, that is, a seconda...

AI Technical Summary

Problems solved by technology

When the engine exhausts, the pressure formed in the exhaust pipe is pulsating pressure. When the exhaust valve is opened, the piston in the cylinder moves upward to push the burned gas out through the exhaust pipe. At this time, the air pressure in the exhaust pipe is positive. When the exhaust valve is closed, a momentary negative pressure is formed in the exhaust pipe, and fresh air is inhaled through the secondary air supply valve to replenish oxygen to the exhaust gas in the exhaust pipe. However, when the engine exhausts, this pulsating pressure is very asymmetrical , the positive pressure in the exhaust pipe is much greater than the negative pressure, and the duration of the positive pressure is longer, and the duration of the negative pressure is extremely short, resulting in a very small supplementary amount of fresh air, which makes the oxygen participating in the oxidation reaction insufficient, and the HC in the exhaust gas 、CO cannot be fully oxidized, and cannot effectively reduce engine pollutants

Especially general-purpose engines because of their small displacement and relatively low speed, the exhaust pressure is much lower than that of automobiles and motorcycle engines with relatively large displacements. When the exhaust valve of a general-purpose engine is closed, the instantaneous negative pressure formed in the exhaust pipe is also It is much smaller than the negative pressure of automobile and motorcycle engines, and the amount of secondary air that can be inhaled by the instantaneous negative pressure is even less. Even if a high-quality three-way catalyst is combined with the existing negative pressure secondary air method to reduce exhaust emissions, its The emission of HC+NOx in the exhaust gas is also 8-10g / kW·h, and the emission of CO is also 350-450g / kW·h, which cannot meet the exhaust gas emission standards set by developed countries, which seriously affects the general-purpose engine as a power machinery product. international sales

And the three-way catalyst must be replaced regularly after being used for a certain period of time, resulting in an increase in the cost of reducing exhaust emissions

How to effectively reduce the exhaust emissions of general-purpose engines and meet the high exhaust emission standards has long been a problem that the engine manufacturing industry wants to solve, but has not been able to find an effective way to solve this problem

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