Languages:
Application:
- Small displacement 2 stroke engines.
Pros’s
- New regulation = new market
- Universal common design
- Only HC and CO conversion is needed.
- NOx is neglible.
Two stroke engines
- The primary emissions from a two-stroke engine are HC, CO, and particulate matter (PM) emissions in the form of white smoke.
- NOx emissions are very low because of the effect of high residual combustion gas retained in the combustion chamber which acts as internal EGR.
- NOx emissions are not regarded as a significant issue.
- Due to the lubrication technology used on the basic two-stroke engines, scavenging also results in high PM emissions.
- The simultaneous conversion of HC, CO, and NOx requires very precise, near stoichiometric, intake charge control that is not possible for typical two-stroke motorcycle engines.
Motorcycle catalyst applications
Two stroke engine applications
- Two-stroke engines emit low NOx emissions, designs focus primarily on effective oxidation of HC and CO and the reduction of white smoke or PM.
- The scavenging losses provide one source of oxygen, but is not enough to achieve 100% conversion of HC and CO.
- In advanced two-stroke engine designs, oxygen availability is improved by adjusting the air-to-fuel ratio to provide a relatively lean intake charge.
- Additionally, a simple passive secondary air injection system (SAI), such as a reed valve, can be installed upstream of the catalyst to provide excess air to the catalyst.
- Another beneficial use of catalyst technology on two-stroke engines is the reduction of white smoke (particulate matter).
- Estimated conversion efficiencies of an oxidation catalyst on a two-stroke engine are on the order of 50% for HC, 50% for CO, and 45% for PM without the use of secondary air.
- The addition of secondary air injection is estimated to increase average conversion efficiencies to approximately 80% for HC, 75% for CO, and 70% for PM.
- While two-way oxidation catalysts are effective in reducing the soluble component of PM or SOF, some manufacturers are developing catalyzed particulate filters for two-stroke 50cc scooter exhaust.
