ARPA-E talks advanced hybridization, carbon-neutral liquid fuels

In the race to place the automotive sector on a sustainable footing, the field is dominated by just two horses: battery-electricity and hydrogen fuel cells.  The economic implementation of BEVs is already well underway, with motor companies on track in 2017 to sell more than a million vehicles globally for the first time.  The economic implementation of FCVs is also in progress, albeit at a much earlier stage, and has the backing of major motor companies and public-sector agencies.  Given the huge leads enjoyed by electricity and hydrogen, ammonia is scarcely seen as a contending fuel.  Earlier this month, though, the U.S. Department of Energy’s ARPA-E unit published an interview with two of its program managers that has an intriguing implication: the race is far from over and ammonia may yet break to the front of the pack.

The ARPA-E program managers are Grigorii Soloveichik and Chris Atkinson.  Soloveichik has been mentioned many times in Ammonia Energy for his leadership of REFUEL, the program that is funding 13 ammonia-oriented research projects.  Atkinson is the Program Manager of NEXTCAR, which is focused on “connectivity and automation to co-optimize vehicle dynamic controls and powertrain operation, thereby reducing energy consumption of the vehicle.”

The central topics discussed in the interview are novel forms of hybridization: on Soloveichik’s side, battery-fuel cell hybridization; on Atkinson’s, advanced methods of battery-internal combustion engine hybridization.  In April 2017, Soloveichik delivered a presentation at an ARPA-E meeting that made the case for his concept (covered here by Ammonia Energy).  Two pairs of numbers were at the heart of his message: 85 kWh vs. 10-20 kWh – respectively, the battery storage capacity of a Tesla Model S and of an optimized hybrid battery-electric/fuel cell vehicle; and 113 kW vs. 5-20 kW – respectively, the power rating of the fuel cell on board a Toyota Mirai and on an optimized hybrid vehicle.  In this schema, the optimized hybrid vehicle would have radically less energy stored in batteries and a radically less powerful fuel cell than what is found on current production vehicles.

The technical rationale for Soloveichik’s concept revolves around the adequacy of two parameters: dynamic torque (power that can be used for acceleration) and driving range.  Torque adequacy is addressed by the fact that a battery’s ability to produce power (kW) is not related to its energy storage capacity.  At full throttle, the Tesla Model S draws 270 kW of electrical power from its batteries.  This could be produced by a 15 kWh battery no less than an 85 kWh battery, albeit in the former case for only three minutes.  As Soloveichik put it in the interview, “batteries, especially lithium-ion cells, are capable of releasing large amounts of power on demand, but with limited energy storage ability.”

The fact that the battery pack can take the lead with the torque challenge allows the fuel cell to be optimized for the range challenge.  A 20 kW fuel cell produces electricity at a rate sufficient to keep up with the typical energy consumption of an electric car traveling at 60 MPH.  (This is based on a reported draw of 329 Wh per mile for a 2011 Nissan Leaf traveling at that speed.)  The hybrid system, therefore, produces the best of both worlds: the peppy acceleration of BEVs and the petroleum-car range of FCVs.

Cost is an inherent challenge for hybrid propulsion.  In classic parallel and series hybrid architectures, an internal combustion engine co-exists with batteries and an electric traction motor.  The complete redundancy of propulsion systems creates an up-front cost hurdle that downstream savings on fuel are hard put to surmount.  But Soloveichik’s concept contains two considerations that create significant economies.  One is the radical downsizing of the battery packs and fuel cells relative to non-hybridized versions of these vehicles.  The other is that battery packs and fuel cells are both elements of an electric propulsion architecture, with the result that the redundancy of systems is far from total.  With these factors in play, a Soloveichik hybrid may prove to have superior lifecycle economics, especially as the cost of fuel cells continues to decline with increasing technical refinement and production volumes.

Atkinson, with a long-standing interest in “increasing the efficiency of energy conversion systems, ranging from engines, to vehicles, to HVAC systems,” believes the same idea could have validity in a hybrid power battery-ICE model.  While the idea of battery-ICE hybridization is anything but new, Atkinson sees untapped but “significant opportunities to create a better experience for the user while saving large amounts of energy.”  He continues, “We’re looking at taking conventional hybrid powertrains to the next level by pairing a relatively small battery with an ultra-high-efficiency engine capable of extending the vehicle’s range far beyond that of hybrids or BEVs today.”  Presumably the type of engine envisioned by Atkinson will be both small (having, for example, a power rating of only 20 kW/27 horsepower) and simple (for example, requiring by virtue of its high-efficiency operation, only a stripped-down emissions control system), such that the cost penalty of system redundancy can be minimized.

Atkinson and Soloveichik emphasize the complementary role that could be played in their vision by a sustainable liquid fuel.  In Atkinson’s mind, the goal is to develop “new energy efficient, low-emissions technologies to leverage their greatest advantages in a combined or hybrid configuration . . . while potentially using existing refueling infrastructure.”  Soloveichik has articulated his thoughts about sustainable liquid fuels on several occasions.  In his keynote address at the 2016 NH3 Fuel Conference, he described the focus of the REFUEL program as “transformational technologies to reduce the barriers to widespread adoption of intermittent renewable energy sources by enabling the conversion of energy from these sources, water and air to energy-dense carbon-neutral liquid fuels (CNLF),” and went on to identify “ammonia, which has high energy content and can be easily liquefied, [as] one of the best CNLFs.”

Atkinson and Soloveichik both have ideas about how to move forward with advanced hybridization.  Atkinson: “We are interested in novel engine architectures, engine configurations and emerging technologies such as integral engine and electric machine design.”  Soloveichik: “To realize this vision, it is necessary to develop novel fuel cell stack designs capable of starting up quickly and delivering high power using liquid fuels, as well as advanced highly capable internal combustion engines with efficiencies well above present-day levels.”

The thinking behind today’s BEVs and FCVs feels immature, similar to how dial-up Internet access to felt before faster forms of connectivity became widespread.  This is not a criticism.  How likely are we to arrive at consummately refined solutions in the first post-petroleum generation of vehicles?  The ideas put forth by Atkinson and Soloveichik feel like evolution in action.  They are explicitly “next generation” in their embrace of batteries, fuel cells, ultra-high-efficiency ICEs, and carbon-neutral liquid fuels as elements that can be combined in affordable and sustainable designs.

ARPA-E is an agency of bold, future-oriented ideas.  It may be that the interview was intended to prepare the way for a new program based on Atkinson’s and Soloveichik’s ideas.  If that proves to be the case, it would certainly be a major step forward for the motor industry and for the United States economy.