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Emerging Technologies in Vehicle Propulsion Systems


In today’s ever-tightening EMS budgets, one of the largest operational costs is fuel. Rescue rigs are required to run nearly 24 hours a day, seven days a week, and that means fuel—and a lot of it.

In recent years, the push in the consumer vehicle market has been to incorporate alternative fuel options to reduce reliance on foreign oil, reduce greenhouse gases and improve operational efficiency. Part of this has been driven by government mandate to increase average fuel economy numbers, but consumers are becoming more educated on the benefits and capabilities of hybrid and alternative fuel sources because technology has advanced enough to them practical for the everyday driver (examples of this include Nissan’s all-electric Leaf and Chevrolet’s plug-in hybrid, Volt).

As this technology goes mainstream, it will become increasingly integrated into the EMS world. But just what is the technology behind hybrid and alternative fuels and how could it affect your daily routine?

Types of Hybrid-Vehicle & Alternative-Fuel Technologies
A number of technologies are trickling into the marketplace, and it can be easy to confuse them. Let’s look at two promising technologies with real-world application in EMS: hybrids and plug-in hybrids:

Hybrid technology is probably most recognized because of vehicles like the Toyota Prius and Honda Insight, which have been around for a few years. The technology is also present in many other vehicles, including General Motors’ pickup and sports utility lineup lineup (e.g., Sierra and Escalade).

Hybrids are a combination of two energy sources, a conventional internal combustion engine and an electric motor. The choice of which powers the vehicle depends on the type of drive train employed. In the first, called series-hybrid, the electric motor is responsible for propelling the vehicle down the roadway. An internal combustion engine is present, but it’s used only to generate power to recharge the high-voltage battery pack.

The second, more prevalent technology is the parallel-hybrid design, in which an electric motor supplements the internal combustion engine for propulsion or provides propulsion on its own. This design can be found in most hybrid systems, including GM’s truck platform, because the vehicle isn’t tethered range-wise by the capacity of the battery system. Instead, the electric motor can be used to launch the vehicle from a standing start, provide power while stopped and assist the gas engine in accelerating the vehicle. The internal combustion engine also starts automatically if battery power depletes to a certain point, which would be commonplace with EMS vehicles that are at scenes for extended periods of time.

Combining the two energy sources creates several advantages. First, because an electric motor generates maximum torque at all times, it can efficiently accelerate a vehicle from a standing start. Second, the ability for battery power alone to power the vehicle at low speeds or when stopped saves fuel. Third, the ability to supplement a gas engine with battery power means a smaller engine can be used, thereby increasing efficiency. Fourth, a technology called “regenerative braking” can be used. Using this type of braking, kinetic energy produced by the brake system is captured and used to charge the brake system.

You may notice I refer to gas engines specifically, and not diesels. It’s possible to have a hybrid-diesel, although that technology is just emerging. However, it holds the most promise for EMS vehicles because of the inherent torque, economy and longevity of the diesel engine. In fact, UPS has been testing six diesel hybrid trucks for the past year in Phoenix. According to futurepundit.com, the diesel-hybrid setup generated a 28% increase in fuel economy, which translated to a 15% improvement in total cost per mile. That’s why UPS has ordered 200 more diesel-hybrid models. This means it won’t be long before either a gas or diesel-hybrid will be making its way into your engine bay.

Plug It In
Plug-in hybrids are similar to hybrids in that they employ two propulsion sources, an internal combustion engine and electric battery packs, but they also include the option to plug the vehicle into a charging source when parked. This allows larger battery packs to be used, which means driving distances under electric power alone can be dramatically increased. When the battery power depletes to a certain point, the gasoline engine kicks in and provides propulsion. This design is also parallel in that both energy sources can power the transmission and drive wheels.

This setup offers several advantages to the EMS marketplace. First, the larger size of EMS vehicles means that there’s space for larger battery packs. Second, because many rescue rigs sit in firehouses where rescue rigs are already plugged to maintain readiness, integration would be seamless. Third, the increased range of the electric propulsion system means that EMS rigs that operate in smaller jurisdictions could run calls on all-electric mode, eliminating fuel costs and emissions. Fourth, diesel fuel consumption can be reduced by as much as 50%. Finally, the absence or limited use of diesel fuel when stopped at a scene means zero emissions, which means not having to breathe diesel fumes.

Fortunately, a plug-in hybrid already exists on a chassis already being used for rescue rig service. Recently, Mercedes-Benz, which also markets its Sprinter van through Dodge, introduced a plug-in diesel hybrid model for service use. The integration of plug-in capabilities means that an electric motor more than twice the size of the non-plug-in Sprinter hybrid can be used. The 70Kw electric motor provides boost to the diesel engine under heavy loads and provides pure electric power at low speeds and when stopped. Another advantage is that the electric motor can also be used to power equipment while in the field. The plug-in diesel hybrid Sprinter is in the first stages of being introduced, but because the Sprinter is already offered in an ambulance configuration, integration into your existing fleet could be accomplished fairly easily.

Other fuel technologies are out there, but the hybrid and plug-in hybrid are hitting the market with applications for EMS duties in the very near future. With their significant increases in fuel economy, reduced emissions, ability to provide electric power in the field and torque advantages, incorporating these technologies into your EMS fleet should rank high on your priority list.


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