Navistar is moving in a different direction, choosing to develop LNG and CNG vehicles. "The beauty of LNG or CNG is they have a completely different flashpoint than propane," says Mann. "They are lighter than air. If you were to run into a CNG truck and the tank got punctured, [the fuel] would just basically evaporate into the atmosphere."
The performance of LNG or CNG is basically the same, says Mann. The difference comes in how it is fueled. Users of CNG tend to have dedicated fueling stations, while LNG doesn't require a dedicated fueling source. "In addition, it is much quicker to fill the LNG than it is the CNG," he states.
Navistar is working with Clean Air Power to transform its MaxxForce 13 into a dedicated gas engine. "They basically put six injectors on the front of the air intake," says Mann. "It runs on a mixture of 15% diesel and 85% LNG. The packaging of LNG is a little more friendly that CNG. It has the advantage of using off-the-shelf components."
Navistar was one of the leaders in the move to hybrid technology with the introduction of hybrid utility trucks, where the engine can be turned off and the body operated with stored electrical energy. This makes a lot of sense in applications where trucks do a lot of starting and stopping, generating electricity that can then be used to run equipment with the engine off.
BAE Systems has vast experience with heavy-duty hybrid drive systems. "We have 3,500 of these systems on buses today," says Mike Mekhiche. "About 3 1/2 years ago, we started looking at the truck market. We spent over a year analyzing the best architecture, particularly the heavy-duty vocational truck market."
The result is the HybriDrive Parallel Hybrid drive system, which has an electric motor/generator located between the engine and transmission. "The automatic transmission is controlled entirely by the hybrid system," says Mekhiche. "The software and shift maps are actually tailored for the application."
There is a lithium-ion storage system. "It is liquid cooled and completely sealed from the environment," says Mekhiche. "A system controller manages energy flow between the wheels and battery... It is a very simple, common architecture."
Unlike many other hybrids, it is designed to withstand the demands of the on/off-road environment. "We have designed this system to be a true heavy-duty propulsion system. The differentiator is we do have a clutch between the engine and electric machine itself," Mekhiche explains. "That clutch allows us to basically separate the powertrain from the engine. Doing that allows us to launch the vehicle electrically without support from the engine. The engine is then revved up to the appropriate speed where it is most efficient. At that point, you re-clutch and connect to the engine." The result is less fuel consumption and lower emissions.
While on the jobsite, you can declutch from the engine and operate equipment on the truck electrically. If you need to inch forward, you can do that without turning on the engine. "It saves a lot of fuel and a lot of noise," says Mekhiche.
Two electric variants are available with a choice of transmissions. "There is a 70-kW (94 hp) with 400 Nm (295 lbs.ft.) of torque and a 110-kW (148 hp) with 800 Nm (590 lbs.ft.) of torque," notes Mekhiche. "Depending upon the size of the vehicle, the vocation and duty cycle, we can marry one of the two electric machines with four different transmissions to get the maximum torque." For a Class 8 construction vehicle, you would use a CX 31 transmission and the 148-hp, 590 lbs.ft. variant. "With that kind of power and torque, you can propel the vehicle electrically without support from the engine.
"We designed it so that it interfaces with engines anywhere between 300 and 650 hp, whether it is CNG, diesel, or gas," Mekhiche continues. "The HybriDrive provides the best performance in duty cycles where you have some level of stop and go. With all types of duty cycles, we are showing an average 30% fuel savings." In addition, the system recaptures energy when you take your foot off the throttle, saving wear and tear on the brakes.