Better Fuel Economy ... From Air?

International has made a major bet on its 11- and 13-liter MaxxForce engines to take the place of current 15- and 11/12-liter power units.

Based on the European MAN D20/D26 architecture, these are tough engines capable of very high power density, and the 13-liter in particular has the potential to transition many 15-liter customers to the smaller and potentially more economical engine.

If you think about piston displacement per mile, if a small engine can produce the same performance as a big one at the same rpm, reducing the cylinder size and hence the amount of air and fuel that goes through it should result in better economy. (Mind you, International has hedged this bet with the development of the MaxxForce 15, based on Caterpillar C15 iron. But that's another story.)

Using a small engine to do the same job as a big one also is the core technology of a hybrid vehicle. Here, though, electric or hydraulic storage of kinetic energy is added to the lower torque of the smaller engine in high-demand situations such as acceleration from a standstill. The big plus with hybrids is that the energy in storage is "free," captured in deceleration instead of being wasted to the atmosphere.

A unique technology that combines some - but not all - of these principles is the new pressure-boosting system from Bendix. It was originally developed to help improve the startability of a new bus order for a rugged, hilly South American bus application. Acceleration on the hill starts was not acceptable for the little 7-liter diesel designed into the buses, but the engine compartment was not big enough for more displacement. Bendix had the answer in the Bendix PBS Air Injection Booster. It was announced in North America last year and re-introduced at the Mid America Trucking Show this year, showing the company is determined to develop the technology and bring it to production - and likely within only a couple of years. Along with the PBS system, Bendix also introduced some additional air management that is immediately applicable and brings its own fuel economy benefits

At the Mid America Trucking Show, in addition to re-emphasizing the benefits of the PBS Air Injection Booster, Bendix introduced the Electronic Air Control (EAC) Dryer and the Turbo-Clutch Air Compressor. Together, all three components can equal up to 8 percent in fuel savings, said Bendix.

Since introducing the PBS air injection technology in 2009, the company has continued its internal validation and field testing. Preliminary results show up to 3 percent savings in fuel with the addition of just the PBS unit - without downsizing the engine.

The PBS engine booster is unique. Residing close to the engine air intake manifold, it monitors the databus (CAN) for specific signals. Once the conditions for activation are met, the system injects compressed air from an auxiliary air tank into the inlet manifold, delivering the desired amount of air to enable early application of fuel to significantly boost throttle response and performance.

Typically, when a driver presses down on the throttle to demand acceleration, there is a delay in engine response because of turbo lag. This lag results from the time difference between acceleration demand and the maximum air delivery as the turbocharger spools up. The Bendix PBS system overcomes turbo lag by instantaneously injecting the desired air into the intake manifold, allowing the turbocharger time to spin up to its full capacity and take over the air delivery demands.

This gives a far faster response to the throttle. It opens the way to a downsize of the diesel engine in applications where acceleration demands are critical or engine compartment packaging is at a premium.

Contributing additional fuel savings, the Bendix Electronic Air Control system is a compact, electronically controlled compressed air control system. The controller integrates the air dryer, unloader valve, multi-circuit protection valve, and has the capability to integrate the park brake mechatronics. Its four primary functions are air quality assurance, pressure control, air distributions defined according to customer priorities, and information management. The sensors enable optimized system control, plus on-board/off-board diagnostics. A commercial vehicle equipped with EAC technology can achieve up to 2 percent in fuel savings, Bendix says.

The pneumatically operated single-cylinder Bendix Turbo-Clutch Air Compressor works together with PBS air injection and EAC, so that the compressor disengages during the portion of the duty cycle when no air is demanded. This greatly reduces power consumption from the engine even when the compressor is unloaded and improves fuel efficiency. As a result of the reduced overall cycling, the life cycle of the compressor significantly increases and normal wear and tear is dramatically reduced, says Bendix.

Bendix is the expert in air systems as is evidenced by the Air Control system, But by launching into engine air management with its PBS it is bringing a new dimension to engine sizing and application. Will we see it on the downsized power units that are seeking to win the crown from the 15-liter stalwarts? I would bet on it.