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Exhaust emissions? They barely exist now. But wait, there’s more to be done.

By on March 2, 2015
AirFlow-truck

It’s been more than 15 years since the EPA started regulating pollution from truck exhausts. It began with nitrogen oxides (NOx), precursors of smog, controlled in 2002 using exhaust gas recirculation (EGR). In 2007, diesel particulate filters (DPFs) and closed crankcase ventilation addressed particulate matter. In 2010, selective catalytic reduction (SCR) cut NOx to levels not even measurable a decade earlier. New testing instruments were needed to assure results.

Overall, emissions were reduced by more than 99 percent. Still wanting more, the EPA turned its attention to greenhouse gases (GHG), so named because they trap solar heat in the atmosphere much like a greenhouse traps heat to help grow plants, fruits and vegetables.

When you’ve taken as much pollution as is technically and economically feasible out of the combustion process, how do you reduce it further? By making the vehicle more fuel efficient. And that takes myriad small steps. Burning fuel creates greenhouse gases, so cutting the need for fuel creates less of them. It’s why EPA’s latest drive is to improve fuel efficiency.

The emphasis has shifted from the engine to the total truck, and progress has come in smaller and smaller steps. When the first aerodynamic shrouds for tractors came out, fuel economy improved as much as 12 to 15 percent. In recent years, reductions in tractor drag have been minimal, each step accounting for 1 to 3 percent at most.

Focus has shifted to the next obvious area for change: trailers. Initial innovations like trailer tails and skirts offered 5 to 9 percent improvement in fuel economy. Today, aerodynamicists are searching hard for 2 to 3 percent gains — or even less.

Where will these increments of better fuel mileage come from? Given a bit of knowledge about a few trends in trucking technology, here are some educated guesses.

Advanced aerodynamics

Aerodynamics will continue to be a focus for truck and trailer builders alike as engineers seek every advantage. Minor adjustments to corners or fairings will account for many small airflow improvements, with corresponding mpg gains. The next big breakthrough will come when tractor and trailer makers partner to develop fully integrated trucks.

We’ve seen these partnerships at trucking shows. The best integration example is the AirFlow Bullet truck built by Bob Sliwa of Newington, Connecticut, displayed at recent Mid- America Trucking Shows. Tractor and trailer together look as if they came from just one designer’s fertile mind. When Sliwa operated his first AirFlow truck in revenue service, he averaged better than 12.5 mpg. He keeps his engine between 1100 and 1250 rpm, but his next truck will operate at lower revs.

Sliwa’s quest for better fuel economy goes beyond the engine and aerodynamics. He is a pioneer in using Truck-Lite LED headlights to reduce alternator load and a computer-controlled Horton viscous fan clutch to control parasitic load.

Reducing wasted energy

dd16-photo-hiresFuel’s latent energy is converted to heat, so engineers are working on ways to keep heat from being wasted through the cooling system or exhaust. Detroit Diesel’s DD16 (at right) brought back a technology from World War II aircraft: turbo compounding. A turbocharger takes heat from exhaust and converts it to mechanical energy to force more air into the intake.

Some of that energy can be transferred to the crankshaft to boost power without hurting miles-per-gallon.

Similar heat recovery turbines can drive alternators for electrical energy without the parasitic drag from drive belts and pulleys. Further reductions of parasitic loss will be realized by electrifying power steering and air conditioning.

When vehicles start cold, especially in winter, it takes time for liquids such as oil, coolant and hydraulic fluids to reach operating temperatures. Exhaust gas reaches temperature almost immediately. Dana recently announced a system that uses hot exhaust to bring fluids up to operating temperatures in a fraction of the time, reducing parasitic energy demands.

Even coatings and waxes are not immune from engineers’ and chemists’ creativity. Whenever two substances move against each other, they create friction that wastes energy. By reducing inter-surface friction you reduce fuel consumption. One manufacturer, DSX, developed a wax that, in SAE/TMC controlled tests, improved fuel economy just over 1 percent. When used on a Formula 1 race car, times were reduced by one second per lap. New greases and oils are being formulated to reduce friction even more.

Changing the oil

Reducing internal friction is also an effective path to improving fuel economy. Some operators have already switched from industry-standard 15W-40 engine oil to 10W- 30. The first number, the one with the “W” for winter, is the viscosity of the base oil. The second number is the viscosity at operating temperature after the viscosity improvers have activated.

With thinner oil, pumping is easier, and the drag caused when crank throws splash-through oil in the sump is lower. Thinner oil means that less energy is needed to lubricate the engine.

As base oils are improved and more synthetics become available, the trend toward thinner oils will certainly continue. Synthetic oils are tougher than normal petroleum oils and have more uniform flow characteristics. The end of the decade will see wider acceptance of 10W-30, with oils as light as 5W-20 eventually taking over the entire motor vehicle market, including heavy trucks.

This does not mean that we’ll pour lighter oils into older engines to get better mileage. Engines will be designed for the new oils, with new bearing materials and higher oil pressures. Tolerances will be tighter and new alloys will control thermal expansion. Improvements in metallurgy and more precise metal forming techniques will lead to more durable engines and oils that go farther between drains.

Thirty years ago, only one-third of the energy generated from fuel was utilized in propelling trucks down the road. The rest was wasted energy. Today, we capture and use about 45 to 50 percent of our fuel’s energy. Many of the big steps toward greater efficiency have been taken, but the creativity of engineers, suppliers and innovators will keep the improvements coming.

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