9 April 2010
Caterpillar shed more light in recent weeks on the emission technology choices for meeting Tier 4i/Stage IIIB standards in diesel engines above 130 kW for industrial and generator set (mobile and stationary) applications. Different technologies will be used—including exhaust gas recirculation (EGR), particulate filters and selective catalytic reduction (SCR)—depending on the engine power category.
The emission solutions in Tier 4i engines will be marketed as “ACERT Technology”. Tier 4i/Stage IIIB industrial engine models recently announced by Caterpillar include the C13 ACERT (287-354 kW), C15 ACERT (354-433 kW), C18 ACERT (448-597 kW), C27 ACERT (597-783 kW) and C32 ACERT (708-895 kW). (The Tier 4i/Stage IIIB ACERT models C7.1 and C9.3 were announced at the Intermat show in Paris in April 2009.)
130-560 kW. Industrial engines with power ratings of 130-560 kW will use the Cat Clean Emissions Module (CEM) for PM control and the Cat NOx Reduction System (NRS) for NOx control. In generator set engines in this power range, PM will be controlled through a “diesel oxidation catalyst and particulate filter with an automated regeneration system”, while NOx will be controlled by “combining a small amount of non-combustible gas with the combustion air”.
The NRS system is based on cooled EGR technology, as apparently is the NOx control system for genset engines. Caterpillar achieved a remarkable marketing success in 2003 by introducing ACERT engines without EGR. While the ACERT engines eventually adopted EGR technology, Caterpillar has been avoiding the term “EGR” in engine marketing. The 2007 ACERT truck engines used a low pressure loop EGR that was referred to as CGI (clean air induction).
No technical details were released on the type or regeneration method of the particulate filter system. However, a fuel burner can be seen in some photographs of the CEM module, indicating that a ceramic, wall-flow filter with fuel burner regeneration—similar to the system introduced in 2007 ACERT truck engines—may be used in Tier 4i/Stage IIIB engines, at least in some models. The fuel burner in 2007 engines appears to have had some technical issues (that may be linked to some of the recalls of C13/C15 truck engines). While Caterpillar decided to exit the US highway truck engine market, the company continued the burner development. In a recent patent application, Caterpillar disclosed a deflector intended to protect exhaust piping from exposure to high temperatures from the burner flame.
560-900 kW. Genset engines of 560-900 kW power rating will use the same NOx control approach that was used in 130-560 kW engines—which appears to be EGR—but will not require aftertreatment due to the more relaxed PM emission limit in that power category. Similarly, industrial engines above 560 kW will not use aftertreatment. Engine models that straddle both power categories, such as the C18, will use aftertreatment in ratings below 560 kW, and no aftertreatment in ratings above 560 kW.
900 kW and Above. Large genset engines above 900 kW will feature low soot combustion techniques, incorporating changes to piston bowl design, injector configuration and turbocharger matching. NOx is controlled via an SCR aftertreatment system including a diesel oxidation catalyst combined with an SCR module, with an air-assisted urea injection system. In addition to the Caterpillar-designed aftertreatment system, a dosing control module, urea (diesel emissions fluid, DEF) tank and air source are integrated into the generator package design.