How to Design a Hyper-Efficient Car

Each year, Transport Canada tallies the country’s most and least economical vehicles. For 2011, the winner is the Toyota Prius, which delivers excellent fuel consumption ratings of 3.7L/100 km in the city and 4.0L/100km on the highway. The Prius is an engineering achievement, but it’s not the most fuel-efficient vehicle in Canada.

That title goes to an extraordinary machine created by engineering students at the Université Laval’s Team Alerion Supermileage.

How efficient is their vehicle? The team competes in the SAE Supermileage and Shell Eco-Marathon hypermileage events for student engineers. The Quebec-based team does more than compete; they win, consistently, with an advanced gasoline-powered vehicle that has recorded fuel consumption figures better than 1,300 km/L.

That’s over 3,000 miles per gallon. The numbers seem impossible: 100 kilometers on less than 3 ounces of gasoline, burned in a single-cylinder reciprocating-piston internal combustion engine.

Team Alerion’s monumental achievement has resulted in a swelling trophy case with three consecutive overall victories in the SAE Supermileage competition, despite the fact that the group operates at funding levels that are easily surpassed by many of the US-based teams.

This year, the team beat second-place University of Ottawa and 21 other collegiate competitors from across North America. On April 19th, the team won the gasoline/internal combustion class of the Shell Eco-Marathon Americas 2011 competition, also for the third consecutive time.

So, how do they do it? Many of the details are a closely guarded secret. Suffice it to say, the project contends with numerous trade-offs and variables between engine, tires, weight and aerodynamics. The most important factor in designing a hyper-efficient vehicle, says team captain Anthony Bernier, is all of the above.

“[The vehicle] has to be as light, efficient and as aerodynamically perfect as possible,” he says. “Some teams have a good engine, but a weaker car, some great aerodynamics but a poor engine. To win, you have to do everything.”

Start Your Engines

Converting the energy locked in fuels like gasoline into mechanical work isn’t new technology. Nickolas Otto’s 1876 engine was revolutionary enough to make his name synonymous with four-stoke spark ignition technology, but it was a refinement of previous designs. What made Otto’s engine historic was its relative efficiency. Today, a full-tilt racing powerplant might be 35 percent thermally efficient, while the engine that spins a lawn mower blade can achieve little better than half that figure.

Like all heat engines, energy (and efficiency) leaks everywhere there’s a thermal gradient to ambient. Losses through hot exhaust gases, heat transfer to cooling systems and to the air in general conspire against super-efficiency.

Even if zero heat transfer were possible, keeping the engine from literally melting is a problem that has never been completely solved. Add friction, plus the complex chemistry of burning liquid fuels under pressure and the efficiency problem is far from trivial.

Surprisingly, the team’s base engine is a 3.5 HP Briggs & Stratton air-cooled single cylinder unit displacing 148cc’s, like millions of similar units powering lawn mowers everywhere. It’s mandated by the SAE’s Supermileage competition regulations. At 29 pounds, it’s a lightweight engine, but the venerable flathead design is decades old. It’s about as basic a starting point for high-technology development as possible and is highly inefficient for performance use.

“It’s very primitive,” Bernier bluntly states about the “spec” engine. “We use only the aluminum crankcase. The rest we throw into the garbage.”