Truck Fuel Efficiency “A Look into the Crystal Ball”

(summarized, with editorial comments, from the 10/2013 issue of Lastauto und Omnibus)

Given that profitability for trucking companies greatly depends on the cost of fuel, innovative technologies are being sought and developed to provide better fuel efficiency, however the cost of technology acquisition is critical.  It not enough for the technology to give a perceived “green” image, it must also pay for itself or more during the purchaser’s vehicle service life (usually between 2 and 3 years).

Fuel Efficiency regulations or “GHG reg.s” are helping to promote significant innovations such as:

Wast Heat Recovery (WHR) or Exhaust Heat Recovery (EHR) whereby additional work is recovered from exhaust and coolant heat energy via Rankine cycle apparatus. The opportunity for energy recovery is significant because truck engines today have a Brake Thermal Efficiency (BTE) of circa 40%, with the other 60% going mostly out the exhaust and cooling systems.  According to Daimler, in the 2016-2018 timeframe an extra 5% could be added to vehicle thermal efficiency with such systems. Two ways of capturing the expansion work of the Rankine cycle are being debated: direct mechanical connection to the drivetrain, or via Diesel-Electric hybrid layout with battery as energy accumulator.

On the other, a combination of other less exotic technologies might yield similar fuel efficiency improvement.

High Pressure Common Rail Fuel Injection

Additional fuel savings are still possible from continued development of Common Rail (CR) Fuel Injection systems.  Advance injection profiles, and higher pressures (up to 3000 bar)  will improve combustion processes and reduce exhaust Aftertreatment (A/T) requirements for an estimated 2% reduction fuel consumption.

Improved Aftertreatment

Improvements for A/T systems continue with use of new coatings and materials for Diesel Particulate Filters (DPF’s) to reduce backpressure. Also, the combination of SCR and PF systems is being investigated to higher temperatures throughout, thus promoting passive filter regeneration.

Pneumatic Boost System (PBS)

Knorr-Bremse’s PBS reduces or eliminates turbo lag and increases low speed engine torque thereby enabling engine “downspeeding”. Lower average engine speeds combined with high low speed torque and appropriate gearing are estimated to enable circa 2% fuel savings.

Selectable or On Demand Accessory Drives

Electrification of many Front Engine Accessory Drives (FEAD) has been done, however not for large fans with high power requirements since in makes no sense in terms of the large size and weight required for the corresponding electric motor.  For large fans, stepped control of viscous technologies is better.  FEAD application for electric drive include: air compressors, water pumps, oil pumps and fuel pumps.

Summary

According to AVL, a combination of the above more conventional “near term” solutions can also achieve a circa 5% reduction of fuel consumption with significantly lower cost. Several electrified accessory drives are currently production ready.

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