22 How to Design a Hyper-Efficient Car Université Laval’s Team Alerion Supermileage soars above the collegiate engineering competition with a radical vehicle capable of better than 3,000 miles per gallon. By Jim Anderton E ach 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. May/June | 2011 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. www.design-engineering.com 23 “It’s very primitive,” Bernier bluntly states about the “spec” engine. “We use only the aluminum crankcase. The rest we throw into the garbage.” Naturally, Team Alerion has made significant changes. In the hypermileage league in which Team Alerion Supermileage plays no one leaves anything on the table, efficiency-wise. The exact engine specifications are a closely guarded secret, but Bernier did reveal that the engine uses a modified head derived from a motor scooter while the cylinder is liner-ed down to reduce the bore diameter. There are few photos of the engine. That’s intentional, says Bernier. “Until last year, we didn’t let anybody photograph it,” he says, citing competitive secrecy. The few images available of the engine show aluminized insulation blankets suggesting that the Laval student team is damming heat in every way possible to extract the maximum out of the fuel’s energy content. The team’s modified cylinder head is considerably freerbreathing than the stock piece while the weak magneto ignition and carburetor fuel metering have been replaced with modern ignition and fuel injection systems. Both are controlled by microprocessor. The engine runs on regular fuel—in SAE competition, it’s pure iso-octane—which is less of a handicap than is generally believed, since the anti-knock additives present in “highoctane” fuels do nothing to increase energy density. Clever engineering of the cylinder head, combined with carefully controlled fuel injection event timing and spark can deal with pre-ignition. The ragged edge of pre-ignition is where the engine spends most of its operating life, effectively lugging at weak fuel/air ratios to extract the most from every drop of fuel. Currently, the engine is strictly metal, but the team is open to alternate materials. “There are no ceramics in the engine,” declares Bernier. “We looked at cylinder coatings last year…maybe in the future.” One interesting SAE rule requires that batteries produce Lacking a wind tunnel, Team Alerion optimized their vehicle’s aerodynamic performance in ProEngineer Wildfire (Creo Elements/Pro). www.design-engineering.com Non-structural covers Firewall Reinforcement for the firewall Structural monocoque chassis Front wheels fixation composite panels Composite panels used as reinforcement for the system Team Alerion’s vehicle shell presents a scant 0.285 square meters of frontal area, a fraction of the frontal area of a Formula One race car. no greater than 1.4A/h, requiring strict energy management of ignition and instrumentation to avoid the need for a powerrobbing on-board generator. “For the SAE competition, we used two batteries,” says Bernier. “One for the ECU and support systems and one for the starter. The electric starter is important because the engine doesn’t run 100 percent of the time. We get running and, when we reach a pre-determined speed, we turn off the engine and coast.” The engine power output is a secret, but the lightweight car can achieve over 50km/h. Rolling Resistance Building an efficient engine is only part of Team Alerion’s winning formula. Rolling resistance represents up to five percent of a street vehicle’s energy loss, so the competition vehicle uses every strategy, from razor-thin, very high pressure and low-hysteresis tires to a tricycle configuration to remove the energy-sapping and superfluous fourth wheel. Even the team’s driver, first year undergrad Audrey Laine, is decidedly petite. To win, every gram counts. There are two key components in the driveline: a centrifugal clutch that allows engine idling and a free-wheel overrunning clutch built-in to the drive hub. Final drive is by chain and the disk brake system is powerful enough to flat-spot the high-pressure tires through the cords. Steering is Ackerman type by yoke with lots of negative camber in the front wheels to reduce frontal area of vehicle. Beyond that, Bernier is tight-lipped. Other than the Michelin low-rolling resistance tires, he states simply, “I can’t tell you.” Engineering a slippery shape Aerodynamic drag is a major efficiency issue for all hypermileage teams. Team Alerion used clever engineering and careful workmanship to craft an aeroshell that’s strong, light and very slippery. The design evolved from the team’s winning 2006/2007 vehicle and reduces an already small frontal area by 25 percent to 0.285 square meters. A Honda Civic, by comparison, has a 1.9 square meter figure, which is good by automotive standards. A Formula One race car has a frontal area of approximately 1.1-1.3 square meters, so the team is nearing the May/June | 2011 24 theoretical limits for a driver-enclosed volume. Skin friction was addressed with a minimal wetted area design, while form drag was managed with a super-smooth surface finish to minimize boundary layer separation. Remarkably, the multiple award-winning final shape was designed and simulated entirely “on screen,” with no wind tunnel testing. Instead, the team designed the shell and simulated performance completely within ProEngineer Wildfire (aka Creo Elements/Pro), which consumed more Canoe manufacturer, Kayaks St-Laurent, helped the team create moulds and a fiberglass display shell. The final carbon-fibre body weighs 11 kg. than 100 hours of processor time to iterate the shape into the optimal design. The verified data was then exported to MasterCam to generate the CNC-required G-code for fabrication using a five axis machining centre. Three weeks of effort, with the assistance of Laval’s Centre de Recherche sur le Bois, resulted in a precise, segmented 385-kilogram wooden buck. The polished buck was used as a positive for team partner Kayaks St-Laurent to fabricate a fiberglass/polyester resin mold, from which a fiberglass/gelcoat display shell and finally a carbon-fibre race shell were laid up. The final, highly polished and painted composite body weighs a scant 11 kilograms. How long did it take to design and build the car? Development is continuous and evolutionary, so there’s really no start or endpoint. By print time, Team Alerion Supermileage will have competed in the Shell Eco-Marathon Europe competition in Lausitz, Germany against Europe’s best collegiate engineering teams. However, only one week away from the team’s departure for Germany, Bernier continued to work on an improved carbon fibre body for the upcoming SAE contest. “I worked on it yesterday,” Bernier said. “We’re laying up the prepreg now.” He predicts significant improvements in the already low frontal area figures with the new shell. According to medieval geographers, an alerion was a mythical legless and beakless bird, but Team Alerion Supermileage must seem more like a bird of prey to the student competition. They have reason to boast, but Laval’s Bernier says simply, “We do a lot with a little.” DE www.alerionsupermileage.ca May/June | 2011 www.design-engineering.com