The pulse charging technology will definitely work on larger engines.
While I was studying the math and physics of pulsejets a few years ago,
I applied them to a large device called a ground level flare. We were
using this flare to burn off excess methane gas at a sewage treatment
plant. The local property owners were complaining about the subsonic
vibrations created when the flare would start to pulse at its resonant
frequency. It would shake the glass in their windows. The engineers
were finishing up their analysis when I told them that I had calculated
the resonant frequency of the pulsing at about 8 pulses per second,
just about a perfect frequency to annoy the neighbors. It shakes the
ground, but cannot be heard. The chief engineer told me that it
actually pulsed at 4 cycles per second. He said, "We sure could have
used you when we designed this thing." I had also calculated the
amplitude of the pulse, based on the mass of air being passed through
the system on each cycle. One of the most bizarre contentions about the
flare was that it would eventually cause an earthquake as it continued
to shake the ground! No way. The amplitude of the pulse was about 1000
pounds repeated 4 times per second. To understand how the pulse charge
technology works, the simplest model I can think of is a single
cylinder engine. Imagine the intake system as a flask or container of
constant volume, resonating at a certain frequency. Imagine the exhaust
system as a similar flask, again resonating at a certain frequency.
Pulses of air are moving back and forth in the intake flask, and pulses
of exhaust gasses are moving back and forth in the exhaust flask.
Imagine a third flask, which is the cylinder. It is continually varying
in volume. The task of the engineer designing a pulse charge engine is
to coordinate the pulses in these three vessels so that a pulse in the
intake system reaches the open intake valve during the overlap period
when both valves are open. If another pulse can reach the cylinder
AFTER the exhaust valve has closed, it will have a supercharging
effect! And the motions of the piston must be taken into account as
well. At at certain point in the power stroke of an engine, the piston
is travelling so fast that it gains little by holding the exhaust valve
closed. Therefore, the exhaust valve must be rapidly opened, to put the
inertia of the expanding gasses to work. This is the initiation of the
exhaust side pulse. The exhaust pulse will rebound from the end of the
exhaust pipe back to the exhaust valve just before it closes. In
carbureted engines, this pulse will drive unburned mixture back into
the cylinder. In direct-injected engines, the fuel will not be injected
until both valves are closed. The intake side pulse is achieved by
rapidly closing the intake valve, sending a pulse back to the entrance
of the intake tract. Analysis of pulse charging is easiest with a
single cylinder engine or in those engines which have one carburetor
and one exhaust pipe for each cylinder. Engines which have intake and
exhaust manifolds will have more complex pulsing modes. However, this
type of engine will have a flatter torque curve, while the former type
will have more peak horsepower. Also, the amplitude of the pulse will
depend on whether the engineer chooses to use the natural frequency of
the intake or exhaust system, or if he intends to use the first
harmonic. A pulse charging system using the natural frequency of the
vessels might have very long intake and exhaust tract lengths and be
difficult to fit into an existing engine compartment. |
