Optimizing the Saab BioPower 100 Concept Engine for E100
7 March 2007
GM’s Saab BioPower 100 Concept, presented at the Geneva Motor Show (earlier post), showcases the first production-based turbo engine to be optimized for neat bioethanol (E100) fuel.
In combining Saab turbocharging expertise with the use of high octane E100 fuel, the optimized 2.0-liter engine from the 9-5 range develops 300 hp (221 kW) maximum power. The standard, unmodified 2.0-liter engine that is the basis for the BioPower 100 delivers peak power of 150 hp (110 kW).
Modifications to the engine management system and internal components enable the engine to exploit the high octane benefits of E100 fuel by using a higher compression ratio, together with more boost pressure. The outcome of this work is peak power of 300 hp and a remarkably high specific power output of 150 hp per liter.
This exciting concept shows the tremendous potential of bioethanol, in terms of both performance and future opportunities to ‘rightsize’ engines.—Saab Automobile Managing Director Jan Åke Jonsson
Running on E100, the concept car’s engine also delivers 295 lb-ft (400 Nm) of torque between 3,000 and 5,100 rpm, with almost 85% available at just 2,000 rpm. This strong and flexible power delivery gives the Saab BioPower 100 Concept car zero to 62 mph acceleration in just 6.6 seconds and 50 – 75 mph (fifth gear) in 8.2 seconds. The standard 150 hp gasoline engine produces 177 lb-ft (240 Nm) of torque from 1,800-3,500 rpm, giving zero to 62 mph in 10.2 seconds and 50-75 mph (fifth gear) in 16.3 seconds.
Behind the enhanced performance is the ability of E100 fuel to resist harmful self-ignition, or ‘knocking’, as the fuel/air mixture is compressed in the cylinder. This attribute is denoted by E100’s high 106 RON octane rating. It permits the use of an engine compression ratio that is higher than normally possible with turbocharging, giving more power and greater combustion efficiency without risk of knocking.
The BioPower 100 Concept’s engine operates with a compression ratio of 11.0:1, compared to 8.8:1 for the standard gasoline engine. This has been achieved by modifying the shape of the piston crowns to reduce the volume of the combustion chamber, thereby raising the engine’s compression ratio.
New software for Saab’s Trionic engine management system, which controls the throttle setting, ignition timing, fuel injection and turbo boost pressure, looks after the different ignition timing and fuel/air mixture requirements of E100 fuel.
More durable valves and valve seats are fitted to the engine, together with bioethanol-compatible materials throughout the fuel system. The only other modification necessary is pre-heating of the fuel. This is required to achieve good cold-starting performance, which is the main reason why bioethanol is currently blended with gasoline and sold as E85 fuel.
In ambient temperatures below 60°F (15.6°C), the chemistry of E100 makes it resistant to vaporization and, as a result, it can be difficult to start the engine. To overcome this issue, the Saab BioPower 100 Concept has an experimental fuel heating system, using small heating elements in the inlet ports downstream of the injectors. When the engine is cold, these elements warm the incoming fuel sufficiently to allow it to vaporize. Shortly after start-up, the function is automatically deactivated.
The high compression ratio allows the engine to generate more torque more quickly, particularly from low engine speeds. On the road, the driver of the BioPower 100 Concept will immediately notice a sharper engine response, with a better low speed pick-up before the turbo is engaged.
On full throttle openings, the turbocharger packs up to 1.2 bar (17.4 psi) boost, without risk of knocking from the high octane fuel. It gives the BioPower 100 Concept driver access to the sort of in-gear performance typical of a modern, naturally-aspirated engine of four liters or more. Maximum boost pressure in the unmodified gasoline engine is 0.4 bar (5.8 psi).
That impressive 150 hp/liter specific power output also indicates considerable potential for engine rightsizing, giving the driver the performance characteristics of a larger engine without incurring its additional weight, greater complexity or higher fuel consumption. In this way, E100 offers significant potential to reduce the displacement of an engine—thereby reducing fuel consumption—while still achieving a desired power level.
The overall fuel consumption of the current Saab 9-5 BioPower engine using E85 is about 30% higher than on gasoline and the optimized BioPower 100 engine is expected to yield a near 10% gain against this. Bioethanol burns at a lower temperature than gasoline, which reduces thermal stresses on the engine and benefits fuel consumption at higher cruising speeds. With the future addition of direct injection and lean-burn technology, E100 fuel consumption can move even closer to gasoline levels.
For optimum energy saving, E100 applications could also be combined with electric hybrid technology, reducing fuel consumption and CO2 emissions still further. This development has already been previewed in the Saab BioPower Hybrid Concept, the world’s first such vehicle to use pure bioethanol. (Earlier post.)
While the BioPower 100 Concept is focused on performance, it still retains a flex-fuel capability and the engine will also run on gasoline, or E85, although power levels are not so high. Trionic monitors fuel quality after every visit to the filling station and automatically makes any adjustments necessary for running on E100/E85 and/or gasoline in any combination.
To handle the increased performance, the BioPower 100 show car is fitted with a limited-slip differential and larger front brake discs (13.6 inches) and calipers, while using the sport chassis settings of Saab 9-5 Aero SportCombi. It also has a dual pipe rear exhaust system, with tailpipes similar to those of the Aero X Concept.
Bioethanol’s simple, fixed chemical composition opens up new possibilities in engine management and control. It consists of just one hydrocarbon molecule, whereas retail gasoline is a cocktail of several hundred different hydrocarbons as well as additives to prevent engine deposits which may not be necessary with bioethanol. It is also biodegradable and will dissolve in water.
As it is a single chemical compound, bioethanol allows engineers to exercise much greater precision in maximizing engine performance. For example, it is possible to maintain an ideal fuel/air mixture (Lambda 1) at all throttle openings without impairing the smooth running of the engine, according to GM.
Saab’s experimental variable compression (SVC) engine, revealed at Geneva in 2000, has played an important role as a test bed for BioPower development work. It has been used to help determine the optimum relationship between compression ratio and boost pressure for the BioPower 100 application.
Bioethanol is a potent, high quality fuel which opens up exciting possibilities in helping to meet the environmental challenges that face us. As the need to reduce energy consumption increases, we are exploring ways to run smaller engines that give relatively high power, with and without hybrid technology. Bioethanol can play a key role in this ‘rightsizing’ process, while also minimizing fossil fuel emissions.—Kjell ac Bergström, GM Powertrain – Sweden president and CEO
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