One topic addressed at the 2015 Green Truck Summit (held in conjunction with The Work Truck Show
®) was the impact of future environmental regulations – such as the
National Highway Traffic Safety Administration (NHTSA) Phase 2 Standards for MD/HD Greenhouse Gas and Fuel Efficiency – on truck powertrains. The general consensus? Barring some unforeseen technological breakthrough, internal combustion engines will be with us for some time to come. However, in order to meet environmental standards, these engines will have to be both cleaner and more fuel efficient.
The list of technologies being looked at to achieve these goals is impressive. Some technologies are already being used, but will be made more effective in the future. Others are in developmental phases or still on the drawing board. The overarching thought that comes to my mind, is that while our industry will be able to meet these future standards, the vehicles will be more complex and more expensive.
The Basics
Most, if not all, vehicle efficiency technologies being brought online will continue to play a role in the trucks of the future. The list of these technologies include:
- Vehicle weight reduction
- Use of low rolling resistance tires
- Improved aerodynamics
- Engine cylinder deactivation
- Automatic engine start-stop systems (idle management systems)
- Variable valve timing
- Reduction of engine displacement combined with more efficient turbocharging systems
- Reduced carbon content alternative fuels (natural gas and propane)
- Systems electrification
In some ways, many of these technologies are counterproductive to one degree or another. For example, weight reduction can be used to reduce total energy demands or to increase vehicle productivity. However, the addition of improved aerodynamic fairings, alternative fuel systems, and advanced idle management systems all have the potential to add weight. The trick is to ensure that the gains created by any one of these technologies are sufficient enough to offset the impact of increased weight, and hopefully still provide a viable return on investment.
Another factor to consider is the impact of vehicle drive and duty cycles on operating efficiency. Technologies such as aerodynamics, low rolling resistance tires, and incremental weight reduction have minimal impact on low speed, low mileage vehicles such as inner-city delivery trucks and utility vehicles. The challenge for both the OEMs and end users will be to match technologies to individual drive and duty cycles to ensure that future trucks meet regulatory criteria and at the same time provide the end user with a vehicle that meets their operational needs at a sustainable cost.
Beyond the Basics
The most direct route to controlling engine emissions is the powertrain. This is where we will see most new technologies being considered. While I have no doubt that the systems discussed at the Green Truck Summit will be effective at reducing fuel consumption and emissions, I am also sure that they will significantly increase the complexity of the powertrains that your mechanics maintain. In addition, increased complexity almost always means an increased price. Price increases are a fact of life and we have dealt with them with technologies such as exhaust gas recirculation (EGR), diesel particulate filters (DPFs) and selective catalytic reduction (SCR).
One obvious way to improve engine efficiency is to reduce the amount of energy consumed when air moves into an engine and exhaust gases pass out. The energy associated with this basic engine function is referred to as “pumping losses”. Turbocharged engines often use some type of heat exchanger system (air-to-air or water-to-air) to cool the intake charge air after it has been compressed by the turbocharger. This cooling increases the density of the intake air which in turn helps to improve the engine’s volumetric efficiency. Unfortunately, pushing the air through the heat exchanger takes energy. Therefore, one of the first changes we will probably see is a redesigned charge air cooling system that improves the air handling into the engine. At the same time, look for new air-cleaner designs which will allow the charge air to pass through more freely while still removing particulates from the intake air.
Once the fuel has been burned in an engine, you need to remove the spent combustion gases. The restrictions associated with this process are referred to as “exhaust back pressure.” The first step is to force the gases from the cylinder through the exhaust valve(s). Look for the increased use of multiple exhaust valves and potentially even totally new valve designs to replace the current poppet valve design in use from almost the entire history of internal combustion engines. Probably the strongest contender for this application is some form of rotary valve; these have inherent issues with factors such as heat expansion and contamination by combustion by-products. This may be addressed through the use of advanced materials such as ceramics, but we will have to wait and see.
Removing the exhaust gases from the engine is just the first step in the overall exhaust process. Everything we do to exhaust gases (mufflers, conventional catalytic converters, DPFs and selective catalytic reduction) all contribute to exhaust back pressure. Ongoing research is underway to improve designs for all components, to help reduce back presser while still allowing the process to function well. In my mind, this is one of the first areas where we will see significant improvements.
To be Continued
There is a long list of additional areas where engine efficiency can be improved, including:
- Improved engine combustion efficiency
- Reduction of internal engine parasitic loads
- Reduction of accessory loads
- Waste heat recovery
Multiple applications/technologies are being reviewed in conjunction with every item on this short list. For example, the reduction of engine internal parasitic loads can include items such as reducing:
- Coolant pumping losses
- Lubricant pumping and windage losses
- Internal friction
- Reciprocating mass
- Valve train operation losses
I will continue this review of future powertrain technologies in the April issue of Fleet Affiliation.
If you would like to discuss this, or any other fleet issue, please call 800-441-6832