Electronic fuel injection has been a great thing for cars and motorcycles. Not only did it put an end to the “stutter-and-stall” behavior of 1980s carburetors set very lean for emissions control, it also delivers reliable turn-key operation. When it’s 10 below and I’m already thinking grumpily of jumpers and extra batteries, my EFI-equipped car just starts and drives smoothly away. Civilized.
For bikes, fuel injection has been through enough generations of refinement that throttle response has become smooth and predictable—free of the sudden cut-in of some early versions. Our fears of Federally sealed black-box operation that could never be re-tuned for a pipe or new cam were banished by digital power-to-the-people in the form of laptop-addressable racing ECUs, and on the street, devices like Dynojet’s Power Commander. For persons willing to learn the necessary skills, it is possible to adapt from available hardware electronic fuel-injection systems for virtually any engine not already so-equipped. By use of separate injectors, gasoline-burning turbo engines can be made to tolerate unusually high boost on demand by injecting alcohol. The extreme cooling effect of the evaporation of the alcohol acts like a “liquid intercooler,” pulling mixture temperature down and preventing detonation. The alcohol also has a higher octane rating than pump gasolines.
Now that we’re comfortable with what electronic fuel injection can do, what next? Walk into any car dealer for a look at GDI—Gasoline Direct Injection. Then look at basic engine specs. GM auto engines with GDI have compression ratios a full number higher than did earlier models with conventional port EFI. Manufacturers are using the resulting higher torque to downsize engines, a leading example being the Cadillac CTS V-Six that now does the job of a previous V-Eight. Ford uses the cooler, denser charge delivered by GDI to allow knock-free use of mild turbocharging (EcoBoost). Again, the result is higher torque.
GDI can do this because a) with no evaporating gasoline in the intake tract, there’s room for more air; and b) the absence of fuel from intake flow also reduces heat pick-up from hot engine surfaces. The result is a cooler, denser charge—and more torque.
The hard part is that the time available for GDI’s fuel evaporation is less than half that available for port EFI. This requires a special injector nozzle—one that injects the fuel extra-rapidly and breaks it into much finer, faster-evaporating droplets. Fortunately, such injector technology had already received a lot of R&D for two-stroke direct fuel injection. The new injectors spray directly into the combustion chamber.
The need for a special injector points to the current problem with use of GDI in higher-rpm motorcycle engines: It’s hard to get the fuel into the cylinder quickly enough and in fine-enough droplets in the short time available in such engines. But the major manufacturers are known to be running GDI experiments, and the U.S. start-up motorcycle maker Motus has given its 7800-rpm V-Four engine GDI.
Another technology that can cut fuel consumption is stratified-charge combustion. Lean mixtures can deliver outstanding fuel economy but are very hard to ignite with an ordinary spark. This problem can be solved by aiming direct fuel injection to make the mixture richer around the sparkplug and leaner everywhere else. Such a non-uniform mixture is said to be “stratified.” Engines can be built to operate in two modes: in very economical stratified-charge/lean-burn mode on part-throttle, and in homogeneous-charge mode when full power is required.
Another high-economy technology getting a lot of R&D just now is HCCI—Homogeneous Charge Compression Ignition—which causes a fully mixed charge to self-ignite by compressing it together with hot exhaust gas from the previous cycle. It offers the possibility of diesel-like fuel economy on gasoline.
Why do cars always get these advanced technologies first? Because the high volume of the auto business can pay the initial R&D cost. Once a new technology is established, it can be adapted for motorcycle use.