An Emissions Solution On Two-Stroke Lean-Burn Engines

The internal combustion engine (ICE) fueled by natural gas has moved in the direction of efficiency and environmental friendliness with lean-burn technology. Cameron’s AJAX®LE uses a CleanBurn™ prechamber type of combustion system that allows for operation with very stable combustion at lean air fuel mixtures.

The lean air fuel mixture reduces the temperature in the combustion process, which greatly reduces the formation of NOx. The lean mixture also provides a more complete combustion process resulting in reduced CO and hydrocarbon levels in the exhaust.

However, in recent years stationary engines have been faced with increasingly stringent air quality regulations. Although lean-burn technology has lowered exhaust emissions, further reductions are now required. One common method for reducing such emissions is the use of a catalytic converter in the exhaust system of the engine. This has been proven effective on 4-stroke lean-burn engines, but until recently the 2-stroke lean-burn (2SLB) engine was only able to demonstrate desired removal efficiencies for short periods of time. Cameron has developed the oxidizing catalytic converter for the AJAX LE 2-stroke engine, lowering carbon monoxide, formaldehyde and VOC emissions for long-term emission removal efficiencies. This provides a solution to further reduce NOx levels with the AJAX exhaust expansion chamber.

Federal And State Regulations
National Emissions Standards for Hazardous Air Pollutants (NESHAP) are emissions standards set by the federal Environmental Protection Agency (EPA). The current standard requires the use of Maximum Achievable Control Technology (MACT) to achieve the following requirements for 2SLB engines:

1. A 58% reduction in CO through a catalytic converter (where CO serves as a surrogate to indicate satisfactory removal of formaldehyde (H2CO) from the exhaust), or
2. Limit the formaldehyde in the exhaust stack to 12 ppmvd at 15% O2 in the exhaust.

This applies to engines rated at +/-500 BHP. The H2CO levels for engines rated at less than 500 BHP have recently been restricted via compliance with NSPS regulations because the regulation of volatile organic compounds (VOC) acts as a surrogate to indicate satisfactory removal of H2CO. New Source Performance Standards (NSPS) are control standards issued by the EPA for criteria pollutants. The standards set forth by the NSPS effective July1, 2008 require Reciprocating Internal Combustion Engines (RICE) rated at 100+ BHP to achieve NOx levels of < 2.0 gm/BHP-hr, CO < 4.0 gm/BHP-hr and VOC < 1.0 gm/BHP-hr. New regulations to take effect July 1, 2011 require RICE rated at 100+ BHP to achieve NOx levels < 1.0 gm/BHP-hr, CO < 2.0 gm/BHP-hr and VOC < 0.7 gm/BHP-hr. Many states require NOx < 2.0 gm/BHP-hr now and a few states such as California and Wyoming already require NOx levels < 1.0 gm/BHP-hr.

Testing
Cameron’s oxidizing catalytic converter is capable of removing more than the required carbon monoxide, formaldehyde and VOC levels with a long duration between cleaning of the catalyst elements for 2SLB engines, which was previously achieved only with four-stroke stationary engines. Successful emissions removal was first confirmed during a 550-hour R&D lab test of the AJAX® oxidizing catalytic converter with a DPC-2802LE engine rated at 384 BHP (286 KW) and 440 RPM.