Matthew Perez, a Mechanical Operations Technician for the Virginia Tech Transportation Institute, sent me some details of a design he's working on, he was a little tired of seeing only electric motorcycles when someone mentioned alternative fuels and he thought he would come up with something that would carry him back and forth to work, a trip of 10 miles each way so he developed this air powered motorcycle concept.
The AirHead engine is the center of his design, everything else seems to be doable and Matthew has much of it worked out. The compressed air is held in 4 standard SCUBA tanks, the frame and suspension all pretty much as you would expect.
So what about the engine? Since Matthew sent a lengthy explanation, I'll let him do the talking:
I designed it from the ground up removing all the things that rob an engine of power. There is no charging system, no oil pump, no transmission and most importantly no over head valves. Everything rolls on sealed ball bearings. The gears in the bottom end for the balance shaft and gear reduction are in an oil bath and the output is essentially direct drive. Omitted from this design was an external dry clutch pack but will be included in consecutive revisions. The cylinder is offset as opposed to centered over the crank for a better rod angle on the power stroke. The cylinder and rings, since they don’t need to support the heat of combustion, will be a composite or ceramic setup most likely. Possible additions will be an air jet supplied by the exhaust tubing which sprays the oil bath on the cylinder walls if needed for cooling and wear resistance. Intake/exhaust is controlled by electronic 24vdc solenoids. This allows the motor to be extremely versatile as well as a 2 stroke having a power stroke every revolution.
The solenoid valves serve many functions. The bike is setup as a drive by wire system. The ecu reads input from front and rear wheel speed sensors, the throttle and the two crank sensors and determines pressure, time and duration. There can be predetermined power level settings which will restrict the max pressure anywhere from 150psi to 750psi. During engine braking only the exhaust valve will be operated and can create back pressure based on bike speed, throttle position and brake pressure. The solenoids are the life-blood of this design. Without them you would not be able to have 700+psi entering the engine because a typically poppet valve/spring setup could not hold this pressure.
In addition to the engines normal function there are plans to use it as an air compressor driven by an onboard electric motor which can be plugged in. During this process the operations of the solenoid valves will be reversed allowing the engine to pressurize the tanks. To reach tank pressures an additional booster piston may need to be added to the assembly. The on board electric motor would also be used for regenerative braking to recharge the battery.
Another interesting point is the rear brake:
There is no rear brake pedal and the rear brake is actuated by the Ecu based on a few inputs. Front and rear wheel speed, front brake pressure and the chassis attitude based on a 3 axis accelerometer mounted in the ECU. This removes all foot controls from the rider as well as giving the Ecu control over rear wheel traction.
As with all design concepts like this, the real test occurs once you begin making hard parts and find out if things work as planned. There is obvious work to do here but it shows some interesting lines of thought.
Any air powered machine, in order to be practical, before actual performance is even considered, is some sort of on board compressor, Matthew took that into consideration here. The ability to recharge high pressure cylinders anywhere along normal roads and streets is pretty minimal. If you have that, then the air engine needs to give you enough performance to make the design worthwhile, his targets are 100 mile range and, for short periods, the performance of a current liter bike. Considering the engine is still purely theoretical, we'll have to wait and see.
Matthew designed this bike to meet his short range commuting needs which is a natural place for any of the alternative energy motorcycles we've seen so far. Once you get out of the city or commuter environment, the old liquid fueled internal combustion engine is hard to beat and it gives the developers of these motorcycles a goal to shoot for. We'll keep watching to see how these plans work out.