Advanced turbocharges key to emissions-era diesels: managing airflow critical; Honeywell chooses VNT and AVNT as technology path for commercial truck diesels - engine technology

Diesel Progress North American Edition, Oct, 2003 by Mike Osenga

In many ways, this era of emissions regulated diesel engines also represents the coming of age of turbochargers, especially advanced technology turbocharging systems. In light of the regulations and the design trade-offs between fuel economy and N[O.sub.x], as well as between N[O.sub.x] and particulate emissions, engine boosting systems have become increasingly critical to future diesel designs.

Obviously, turbocharged diesel engines are not a new concept, but as the emissions box continues to shrink globally, new and more precise engine-boosting systems, in a variety of designs and concepts, are coming into the marketplace. And VGT--variable geometry turbocharging of all different types--are right at the heart of those developments. There are certainly more turbochargers in the future for all sizes of diesel engines.

Honeywell's turbocharging unit, Torrance, Calif, one of the diesel industry's major suppliers of turbocharging systems, has selected VNT--variable nozzle turbine and AVNT--advanced variable nozzle turbine for its GT35-40 turbochargers and the double axle GT42 and GT45 models, as its primary technology paths for commercial truck sized diesel engines, in the 200 to 600 hp range.

"For engine manufacturers using EGR for N[O.sub.x] reduction and particulate traps for PM reduction, VNT has an important role in driving EGR, in accommodating the airflow, managing the airflow, while driving the EGR," said Steve Arnold, Garrett's director, innovation and new concepts at Honeywell's turbocharging unit.

"When you introduce EGR to the engine, the engine still needs the same amount of fresh airflow, but you are now moving a lot more gas flow through the engine and you have to find a way to do that. With VNT technology you can maintain the same amount of airflow and also drive the EGR."

For larger engines in the commercial truck range, Honeywell has continued to develop its existing double axle variable nozzle turbine turbos that range from the GT42 through the GT45 models.

The non-VNT GT47 to GT55 product family, now incorporates an upgraded bearing system, as well as aerodynamic improvements and are custom matched for commercial applications to 700 hp. Recent developments in aerodynamic design allow for an inertia reduction of up to 25 percent, according to Michael Cirone, director, commercial diesel product line at Honeywell.

The top end of the range, the Garrett GT60-70 turbo family, now features two compressor designs and three wheel sizes to cover a wide range of pressure ratio and flow requirements.

Smaller output engines are being served by VNT turbos with wastegate options. The Garrett GT15 compact turbocharger is specifically designed for small displacement diesel and gasoline engines in passenger cars, light-duty trucks and marine applications. The GT15's application range is for 1.3 to 1.6 L (60 to 80 bhp) diesel engines and 1.0 to 1.4 L (85 to 120 bhp) gasoline engines.

But it is in the middle, Garrett's GT30 to GT45 range, especially in commercial vehicles, tracks and buses, where much of the excitement is today. Honeywell is currently in production with AVNT versions of ira Garrett GT35, 37 and 40 turbochargers on International's 6 L V8 and 8.7 L, in-line six-cylinder medium-duty diesel engines with a fourth installation due to be announced shortly. The turbochargers are manufactured at the Honeywell turbocharging unit's new facility in Mexicali, Mexico.

Arnold said the design of the three AVNT turbos is very similar, using many of the same components sized to the specific requirements of the turbocharger model.

Honeywell started down the AVNT path in the mid 1990s as the next step in providing optimum airflow for diesel engines. "The idea behind the development program was to create a new value proposition for the customer with variable geometry turbocharging," Arnold said. "For commercial diesels, we had a very good VNT, however the value proposition wasn't sufficient to drive it forward based on fuel economy, drivability and performance."

Arnold said Honeywell approached the AVNT project as a complete system design with an eye on developing a simple, high performance variable nozzle turbine with integrated electronically controlled actuation and position feedback.

The result was an AVNT design that includes a compact turbine housing, integrated actuation, no external actuators, no brackets and 59 percent fewer parts in the turbine housing assembly compared to earlier designs. The turbochargers utilize molded-in-metalmetal injection molding and powdered metal technology to eliminate machining on smaller parts.

One of the keys in AVNT design is the variable geometry mechanism itself, a hotly debated technical subject. For its AVNT, engineers at Honeywell decided on a pivoting synchronized cascade of vanes. The vanes rotate by way on a shaft that is pressed into the turbine housing.

A ring, which moves the vanes in unison, was designed to interface directly with the vanes through a tab-and-slot arrangement. This, Arnold said, eliminates the need for a shaft to penetrate through a cavity and for an arm or gear to be welded or attached to the vane assembly.