31 March 2005
Caterpillar 2007 engine technology—as anticipated—will be based on the ACERT platform with the addition of a diesel particulate filter (DPF) for PM control. In a somewhat surprising announcement made yesterday, Caterpillar indicated that the addition of exhaust gas recirculation (EGR) to the ACERT package will be also necessary to meet the 2007 NOx requirements.
The Caterpillar heavy-duty engines for 2007 will use existing ACERT Technology, which includes series turbochargers, variable valve actuation, a high pressure multiple injection fuel system, Cat® electronics control systems and an oxidation catalyst, said Caterpillar. In addition, all 2007 engines will also utilize EGR, closed crankcase ventilation system, and a DPF system with active regeneration. Mid-range engines will be also build on ACERT technology and feature a high-pressure injection system and the closed crankcase ventilation, with the addition of a variable turbine geometry turbocharger.
The ACERT package was introduced in 2003, to meet the EPA 2002/2004 NOx emission requirements. In contrast to 2002/2004 engines from other manufacturers, the ACERT technology did not utilize cooled EGR for NOx control. Instead, it relied on an advanced proprietary combination of in-cylinder NOx control techniques, possibly including elements of partial HCCI combustion and internal EGR.
The Caterpillar 2007 DPF system uses a wall-flow filter, which is regenerated by periodically heating the exhaust gas using “auxiliary means”, said Caterpillar. Engines with 500 hp or less will require one diesel particulate filter; engines with 550 hp or more will require dual filters. In a 2007 prototype showcased earlier, Caterpillar used a catalyzed cordierite filter, regenerated through injection of fuel into the exhaust system, upstream of a warm-up catalyst. The engine was calibrated to produce high exhaust temperatures, but no in-cylinder post-injection was used, as it is common in passenger car filter systems.
For achieving additional NOx reduction to meet the 2007 requirements (about 1.2 g/bhp-hr, based on phase-in provisions of the 2010 limit of 0.2 g/bhp-hr), Caterpillar introduced a low pressure loop EGR system, where the exhaust gas drawn downstream of the particulate filter—cleaned from the particulates—is recirculated into the intake air. Caterpillar named the technology the Clean Gas Induction (CGI), thus, avoiding the usage of the term “EGR” in the context of ACERT engines, which have been competing against EGR-based technologies (incidentally, the acronym CGI also stands for the Compacted Graphite Iron engine block technology, which may or may not be used in 2007 Caterpillar engines). EGR systems in engines without DPFs typically employ high pressure loop EGR configuration, where the EGR flow taken from upstream of the turbine carries particulate emissions, which presents a potential engine wear issue.
The 2007 PM emission standard is 0.01 g/bhp-hr, down from the today’s limit of 0.1 g/bhp-hr. Additionally, in the 2007 rule, crankcase emissions are regulated as exhaust emissions. The regulation also requires an onboard diagnostic system to monitor the performance of the engine’s emissions system. This industry standard, called Engine Manufacturer Diagnostics (EMD), will detect issues within the emissions control system.
Source: Caterpillar (press release)