Legislative Constraints for Large Diesel Engines and Transmissions for Trucks and Buses

In this article, I will look into heavy duty diesel emission requirements, unique heavy duty diesel issues, particulate filters, and the regeneration of particulate filters, the future of heavy duty vehicle trends, electric hybrid energy recovery, electronic system opportunities and hydrogen fuel cells for heavy vehicles. Please feel free to skip to the parts most relevant to you.

Heavy Duty Diesel Emission Requirements

For heavy duty diesel engines, they are tested on engine dynanometers rather than on a rolling road dynanometer. This is because one particular engine could find its way into many different types of lorries, trucks, tractors and son on. Therefore, it is more cost efficient to test the engine rather than the vehicle. The engine emissions are tested rather than the vehicle. The single duty cycle tests have a lot higher load factor than cars too.

Unique Heavy Duty Diesel Issues

  • The engines will be working at high load factors most of the time.
  • The fuel efficiency of trucks and buses are a primary user requirement unlike it is for cars (where the primary user requirement is aesthetics).
  • Gradients are significantly more important to large vehicles both in climbing and descending.
  • A small percentage of improvements are worth thousands of pounds on an annual fuel bill for large heavy duty vehicles. This is much more significant than on cars.
For heavy duty vehicles, the NOx (nitrous oxides) emissions are the most challenging to control. The US limit for heavy duty trucks from 2007 with stringent implementation requirements from 2010 include:
  • Particulate Matter (PM) - 0.01g/bhp-hr
  • NOx - 0.20g/bhp-hr
  • Non-Methane HydroCarbons (NMHC) - 0.14g/bhp-hr
Euro 6 limits are even more stringent from 2014 onwards.

The technical solutions to meet low NOx limits on heavy duty vehicles consist f:
  • Exhaust gas recirculation - This is the process where some of the exhaust gas is reused in the combustion cycle. This has the effect of reducing NOx levels produced.
  • Urea selective catalyst reduction - This is a liquid additive to increase catalytic reduction of NOx. It requires auxillary liquid tank to carry the urea and requires ultra low sulphur fuel (below 15ppm).

Particulate Filters

Particulate filter objectives are to remove microscopic carbon particles from the exhaust gas (less than 100 nanometres large). This is because the microscopic soot particles can be carcinogenic (cause cancer). The filters can be ceramic, metal matrix or paper - ceramic and metal matrix filters require periodic regeneration to burn off excess carbon.

Particulate Filter Regeneration

Particulate filter regeneration requires the drive cycle strategy to periodically burn off excess carbon to avoid the filter becoming clogged and causing excess exhaust back pressure. This process uses excess fuel to burn the carbon in combination with air from the atmosphere to form into carbon dioxide. Electronic control of regeneration is based on the mileage since last regeneration, engine load factors and vehicle speed. It can adversely affect overall vehicle fuel economy if the user generally drives at low speeds (particulate filter regeneration most efficient at prolonged motorway speeds).

Future Heavy Duty Vehicle Trends

Stop/start technology as well as regenerative braking (recovery of kinetic energy otherwise dissipated as heat in friction brakes) could be introduced. However, the storage of the energy from braking is the main challenge due to the large amounts of potential energy that can be recovered. Forms of energy to store the regenerated braking energy could be:

  • Battery
  • Mechanical flywheel
  • Electric flywheel
  • Supercapacitors
  • Hydraulic
  • Pneumatic

Electric Hybrid Energy Recovery

Electric generator is driven by the wheels and may be wheel mounted or in driveline. Electricity generated needs to be regulated into a form suitable for charging a battery. The battery capacity and type are major factors in determining the storage capacity, weight and transfer rate of energy. Packaging has to also be large enough for large batteries on heavy vehicles which may compromise load carrying capacity.

Electronic Systems Opportunities 

There are many electrical systems that can be beneficial to heavy duty diesel engines such as:
  • Cruise control
  • Speed control
  • Congestion avoidance using real time satellite navigation, route planning and road data.
  • Active safety technology
  • Electronic engine and transmission controls to optimise fuel economy.

Hydrogen Fuel Cells For Heavy Vehicles

This will prove to be a major challenge since the storage of hydrogen to give the adequate range is a huge limiting factor for this new technology. As well as this, the packaging storage tanks and cost are more challenging than for cars. Saying this, it may be a long term solution.