Combining electric powertrains with turbine technology benefits the bottom line.
By Arlan Purdy
Across the U.S. and around the world, ambitious plans to reduce emissions are challenging the limits of conventional transportation technology. Class 8 refuse collection vehicles are the perfect storm of poor fuel economy, poor emissions controls performance and high maintenance costs. Cities everywhere are demanding something better. The challenge now is finding a solution that works in the toughest on-road duty cycle without breaking the budget.
Many proposed solutions require expensive and expansive changes to infrastructure—prodigious new production of alternative fuels or additional grid energy and expensive access points in the form of fueling or charging stations. Many also necessitate public subsidies to make the numbers work. This is a risky bet when headlines announcing new clean energy programs are matched by those announcing budget crises at all levels of government. Among the array of new vehicle technologies on the market is one designed from the outset for frequent-stop, heavy-duty drive cycles. Additionally, the solution is also compatible with current and future energy infrastructure, is compliant with emissions regulation, and achieves a payback independent of fickle government programs. By leveraging the same gas turbine technology that serves as the backbone of the modern electrical grid, it is now possible to combine all the advantages of an electric vehicle (EV) without sacrificing range, power or payback.
Piston Engines Struggle in the Modern World
For generations, the conventional piston engine has been the only viable solution for medium- and heavy-duty vehicles around the world. Diesel engines are so entrenched in our daily lives that many homeowners rely on the familiar thrum of a diesel piston engine making its way through the neighborhood to remind them to take out the trash.
With the introduction of emissions controls, modern diesel engines have greatly improved over the black-cloud belching trucks we might remember from our childhood. But these advances come at a cost, increasing both upfront purchase price and ongoing maintenance expenses. Fleet operators report that emissions control systems now rival tires as the highest maintenance cost. According to the International Council on Clean Transportation (ICCT), selective catalytic reduction systems can cost upwards of $3,661 per engine.
Like diesel engines in general, current emission controls technologies were developed primarily with long haul trucking applications in mind. However, in vocational applications like refuse collection, diesel systems jeopardize performance and cost more. Internal combustion piston engine technology remains widespread today in part because it can serve as a “jack of all trades,” delivering adequate performance under a variety of conditions. However, as customers and regulators demand ever more optimized performance, the need for specialized technology suited for each application increases.
Battery-Only Heavy-Duty vehicles Need Help
Electric vehicles (EVs) have been around as a concept longer than piston combustion engines. In decades past, the challenge has been in providing electrical power to a motor that’s on the move. Built-in power is the obvious answer, but high infrastructure maintenance costs and lack of flexibility have largely limited this approach to subway systems. Meanwhile, the use of other forms of built-in power, such as overhead catenary lines, has decreased. And while subways, trains and trolleys can be established as the main arteries of a transportation network, refuse trucks must serve every street in every neighborhood.
Fast charging technology poses an analogous challenge. While there is less physical infrastructure to maintain, widespread use of fast chargers poses a similar hurdle to the electrical grid as turning on fire hydrants all across a city would have on water supply. Battery banks in charging stations solve the problem of demand surges, but compromise the chances of achieving payback without subsidies.
Simply adding batteries to the vehicle eventually decreases carrying capacity and increases costs beyond what can be recouped with fuel savings. A heavy-duty vehicle, such as a Class 8 refuse truck, requires approximately 10x the energy of a typical passenger car to travel the same distance. Despite advances in battery chemistry, today’s best batteries still only store about 1/100th of the energy of fossil fuels. Additionally, the batteries best at packing in energy per pound exchange added energy for a shorter life, and may need to be replaced well within the working life of a heavy-duty vehicle.
Tomorrow’s Fleets Use Proven Technology
Under these new demands, turbine technology has come into its own. Like piston engines, turbine combustion engines have been in use for decades, mostly in aviation and in grid-scale power generation. To be efficient, generator turbines must run at very high RPM, about 20 times faster than a piston engine. These high rotating speeds are fine for generating electricity or jet propulsion, but the complex gearing required to translate this to a proper wheel speed makes turbines an infeasible direct power source for road vehicles.
With modern manufacturing, however, it is possible to build a microturbine generator small enough to be mounted on a vehicle. It serves not as a replacement for the wheel-cranking power of a conventional piston engine, but as a micro-grid generator—a tiny version of the power plant that might be providing electrical power to homes and businesses in your neighborhood today.
When you redefine the job of the combustion engine from providing power across a range of wheel speeds to recharging batteries efficiently with a minimum weight penalty to the vehicle, a microturbine emerges as the clear winner. While a turbine engine would be even less efficient than a conventional engine at low RPM, as a dedicated, onboard, turbine generator, it can provide the required power with a far lighter footprint than a piston-engine generator. Electric motors, which have been providing high torque at low RPM to diesel electric locomotives for generations, actually drive the axles.
The ICCT estimates that as of 2015, electric powertrains constituted around 1 percent of the U.S. medium- and heavy-duty truck market. Both high upfront costs and a longer return on investment (ROI) have restrained operators from deploying electric powertrains. However, relying on a turbine to produce electricity stored in a battery pack and using that stored energy to power the electric motors makes it possible to effectively double the range of a conventional diesel-powered truck without reducing the carrying capacity or range. This is possible with a payback period of fewer than five years without accounting for any subsidies.
Meeting City and State Mandates
Garbage trucks spend the most time where the most people live and perform the three tasks at which conventional piston engines are the least efficient: idling, stopping or accelerating from a stop at low engine RPM. Most emissions standards are designed for conventional vehicles and are written based on power output of a conventional engine at its best—not at its worst, as in the refuse collection drive cycle.
A turbine engine can be designed to meet emissions standards without the costly exhaust treatment required for conventional piston engines. Because regulations are written based on engine size, a conventional vehicle engine has to be sized for the maximum power needed. However, since the batteries on a range-extended EV system can provide occasional high power, the generator only needs to be sized for average power output. In terms of emissions per ton moved, the turbine is far more efficient. Depending on what power generation source supplies the local grid, the fuel-agnostic turbine range extender can be cleaner than a pure-battery EV.
The mix of emissions is important to understand as well. While CO2 is absorbed in the natural plant lifecycle, diesel particulates, nitrous oxides, and other emissions are directly harmful to human and animal life. The lean burn combustion process in a turbine significantly reduces these harmful emissions, achieving about a 90 percent reduction in comparison to a conventional waste collection truck. High regenerative braking can virtually eliminate residues brake pad particles, a less-discussed contaminant of conventional vehicles.
These systems can also reduce noise pollution. The low-pitch rumble of a conventional diesel engine contributes to traffic noise of about 85 dB, according to the California Department of Transportation. Turbines generate a higher pitch, which is easier to muffle, allowing for both a noise reduction when the turbine is running and an even greater noise reduction when the vehicle is running on battery power. By reducing noise pollution in urban and suburban settings, quality of life overall is improved, and these heavy trucks can operate in a quieter, friendlier atmosphere.
Fuel Savings Translate to Cost Savings
Fuel savings always depend upon the driving conditions, but in frequent-stop, urban refuse collection, range-extended EV fuel savings are estimated to be 67 percent that of a conventional piston engine diesel. Achieving these savings depends upon a high-power regenerative braking system that can efficiently capture the large pulse of electrical power generated by quickly stopping a heavy vehicle. With brake wear virtually eliminated, a set of pads and rotors could last the life of the vehicle. Accounting for additional savings resulting from eliminating exhaust treatment systems, routine oil changes and mid-life engine overhauls, the increased upfront cost of a turbine generator range extended EV can be offset in less than half the working life of the vehicle. This delivers net savings through the second half of its 10 to 12-year service life.
While state and local agencies are moving toward stricter emissions regulations for waste collection vehicles, incentive programs to assist with compliance are not always available to cover an entire fleet through the operating period required to achieve a compelling payback. For privately held waste and recycling companies like The Ratto Group, achieving a payback based on fuel and maintenance savings without relying on future availability of government programs is a critical factor in selecting the right technology for its fleet.
Tailored Technology for a Better Fit
Some EV systems get by with less power or range than the conventional system they replace, based on the specific application requirements. Compromise is not an option for refuse collection. Many refuse collectors are private operators; they must keep their expenses in balance with their income. Since they are paid for each pickup stop, but must pay landfill fees for each trip to the dump, any reduction in range or carrying capacity is not acceptable. Additionally, collection trucks must climb every hill, some with the steepest streets in the world, which can reach grades of nearly 40 percent. As a result, a job-ready EV must have the power to climb the grade and a minimum range to meet the longest route on the map.
Innovation often involves combining concepts already on the market in a way that delivers a service more efficiently than before. Turbines are a proven technology ready to work today by unlocking advantages of electric drive without necessitating that we rebuild our cities with a new energy infrastructure. By completely replacing the conventional engine and exhaust systems, the turbine solution can be retrofitted into an existing chassis to extend the life of an asset, or fitted to a new chassis ready for an alternative powertrain. Original equipment manufacturers (OEMs) can choose whether to meet customer demand by installing the powertrain at the factory or by relying on a third party.
A New Kind of Hybrid
Combining the power of a diesel-electric locomotive with the reliability of an aircraft engine produces a new kind of hybrid, one that’s not afraid of hard work but leaner and cleaner than the old standard. Tomorrow’s fleets combine the best technology for traction power with the best technology for electrical generation in a powertrain that is tailored for frequent stop, low speed, high-power vocational duty.
Arlan Purdy is Product Manager at Wrightspeed (Alameda, CA). With an acute focus on the understanding of how things work, Arlan manages product development and commercialization for Wrightspeed’s the Route™. At Wrightspeed, Arlan works closely with the company’s world-class engineering team to define product requirements and strategically align them with the company’s growing portfolio of global customers. He can be reached at [email protected].