Engines & Emissions
New HDT department will keep you abreast of all the latest engine and emissions developments.
There was much confusion surrounding the introduction of the new engine technologies developed to meet the Environmental Protection Agency's accelerated deadline of just a year ago. There is potentially even more puzzlement going into the next round of emissions reductions that will phase in between 2007 and 2010.
To help Heavy Duty Trucking readers fully understand and get comfortable with what is coming down the pike, we will be running this monthly department, Emissions Authority, designed to keep you current.
This report on Caterpillar's ACERT technologies - along with driving impressions of the C9, C13 and C15 engines - launches the new section, which will keep you abreast of all the latest engine and emissions developments.
Steve Sturgess
Senior Editor
Cat Puts ACERT On The Street
On schedule, but a year late by EPA's deadline, Caterpillar is easing its '02 compliant engines into production with Advanced Combustion Emissions Reduction Technology. As Cat's Customer Value Manager Bob Keene pointed out in an exclusive presentation to HDT, ACERT is a systems approach to reducing NOx and particulate matter (PM) to the level demanded for the EPA's 2004 limits that were pulled forward 15 months. These limits insist that total NOx and non-methan hydrocarbon be reduced to 2.5 g per hp-hr and PM to 0.10 g per hp-hr.
The components of the Cat system are the electronic controls, the fuel system - the injector in particular - the air handling components, a unique variable inlet valve timing and exhaust aftertreatment. These together reduce NOx in the combustion process by lowering the peak combustion chamber temperature - which addresses the NOx formation - and then cleaning up the PM in the exhaust stream using a catalytic converter tucked, in most cases, into the muffler.
The injectors, while new for ACERT, are already in use on current engines. The hydraulically actuated, electronic unit (HEUI) is a fundamental part of the fuel system that is used on the C7 and the newly introduced C9, and shares a family relationship with the HEUI system on International engines. Pressure for the fuel injection is generated hydraulically from a lube oil supply at high pressure, with a pressure amplifier built into the injector.
The mechanically actuated electronic unit (MEUI) injector for the C11, C13 and C15 engines is already in service in the Cat Bridge engine.
Both injectors allow for higher fuel pressure and a pilot injection, which initiates the combustion process. Further, the injectors also allow for rate-shaping, which also contributes to the combustion control, as does the newly shaped piston bowl.
The air system differs according to engine family, too. The C7 and C9 have a single turbo with a "smart" wastegate. The bigger engines all have series turbocharging, which together raise the inlet charge pressure to as much as 42 psi. Series turbos are used because it keeps pressure ratios and turbine speeds down - both contributors to longer turbo life. Air exiting from the high-pressure compressor feeds directly into a water/air pre-cooler, then through the chassis mounted air/air charge cooler to the inlet on the opposite side of the head.
In the case of the C11 and C13, this has meant a change to a cross-flow head design, already a feature of the C15. These units have a fairly simple waste gate to fine tune boost.
An interesting feature of the twin turbos is the flexible steel couplings used to accommodate the differential expansion of the components making up the air system.
A component of the air system not obvious from the outside of the engine is the variable valve actuation (VVA) of the inlet valve on the C15 and the inlet and exhaust on the C11 and C13, controlled by the electronics and acting hydraulically.
On the exhaust valves, the lift is solely to operate the Cat engine brake and, in the future it will also migrate to the C15. The inlet side is hydraulically operated to vary the inlet valve timing and duration. Cat is not saying exactly what this does, though Keene did say that the engine is not running a Miller cycle as has been rumored.
Undoubtedly, the ability to vary the inlet valve timing contributes to the engine's good performance, especially at low rpms.
All this is orchestrated by the electronic controls, which gain several additional sensors on the engine.
The exhaust aftertreatment is a catalyst that combusts the PM. As such, it has to be mounted within a certain distance from the turbo outlet. In a dual stack configuration the oxycat fits into the lower section of the standard-looking muffler. In operation there's no more heat, either, despite the oxidation of CO, hydrocarbons and other soluble organic fractions that make up PM into carbon dioxide and water.
Cat's aim in the development of ACERT has been to design a robust and durable system around proven components. To this end, the system has proven parts: The oxycat is already in use with 80,000 in service; the injectors are already running in Cat engines; turbos are off the shelf. What is new is their combination into the ACERT system, says Bob Keene.
Sidebars
C9 Has Decent Performance
On the Road with ACERT
