How and Why Internal Combustion Works, Part 1

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					        Racing Technology                                 with Evan J. Smith



How and Why Internal Combustion Works, Part 1
Illustrations by John McBride


I  t’s safe to say that most drag racers
   become addicted to the sport after
hearing the roar of a high-power V-8 or
after watching a wild hot rod launch
with the wheels up. At some point,
each of us got the chance to get
behind the wheel (or the wrenches) —
that’s when the real fun begins and
the addiction grows. Drag racing is
indeed addictive, and it doesn’t take
long to yearn for more power, harder
launches, and lower elapsed times.
    With the exception of a few
electrically powered drag vehicles, our
beloved acceleration relies on internal
combustion to propel us downtrack.
More power equals better acceleration
and greater top speed, so we’re always
on the hunt for those precious ponies.
Most racers can rattle off a list of
high-performance engine parts that
will usually help achieve greater power
figures, but there are plenty of people
who do not understand exactly why
these gains occur.
    We’ve all heard the engine is
nothing more than an air pump, and
this is partially true, but the exact
function of internal combustion is a
little more technical and complicated.
    In basic terms, the engine is a tool            which are forced down the bores,                    mystery gas; instead, it provides           what happens to fluids (remember,
used to harness the energy released                 thusly transforming the up and down                 additional oxygen to the combustion         air is a fluid) under changing
from burning a precise mixture of                   motion of the pistons into a rotating               process. Sticking with natural              pressure conditions.
hydrocarbons (in most cases gasoline)               force at the crankshaft. The repetitive             aspiration, we can increase the                To understand what takes place
and oxygen. A fuel source, such as                  cycle of cylinder after cylinder burning            displacement of the engine, we can rev      inside the engine, let’s look at typical
gasoline or methanol, is mixed with                 fuel and oxygen creates a seamless                  it higher, we can (of course) add           four-stroke engine operation. Starting
oxygen (at the proper ratio by a                    flow of power and a nice rumble from                aftermarket components to improve           the cycle, the piston will head down the
carburetor or EFI system) and is then               the exhaust system. But how do we                   efficiency, and/or we can make the          bore. Since the piston is accelerating at
ingested into the engine, where it is               increase the power?                                 existing engine run more efficiently by     great speed, it will create a pressure
compressed and then ignited. The                       Over the years, we’ve learned a few              reducing parasitic drag.                    drop within the cylinder as compared to
rapid burning (not exploding) of the                ways to increase power from the                         But this still doesn’t answer the       the pressure in the intake manifold. So
fuel/air mix expands in the cylinders               beloved internal-combustion engine.                 question of just how oxygen and fuel        when the intake valve opens, the air/fuel
with a resultant release of heat energy             We can do it unnaturally by using                   makes it to the cylinders. For this,        mixture rushes in to fill the void and
and force. The extreme force (cylinder              some form of supercharging. We can                  we can thank Mother Nature and a            equalize the pressure. We call this the
pressure) is applied to the pistons,                also use nitrous, which is not a                    few early scientists who figured out        intake stroke.




(Above left) During the intake stroke, the piston goes down the bore. This creates a pressure drop      (Above left) Just before the pistons reach top dead center, the spark plug fires and
in the cylinder (relative to the pressure in the intake) so when the intake valve opens, the air/fuel   the mixture ignites. As the oxygen and fuel burn, energy is released, and the
mixture rushes in. However, there are many factors that determine how much air and fuel make            expanding gasses force the piston down the bore. It’s commonly known that higher
it into the cylinders. (Above right) On the compression stroke, both valves are shut and the            compression ratios produce higher cylinder pressure and greater power. (Above
pistons compress the mixture into the combustion chambers. Naturally, more air and fuel                 right) Lastly, the piston will cross bottom dead center, the exhaust valve opens, and
(actually oxygen and fuel) ingested means there is greater potential for horsepower to be made.         the hot exhaust gasses are expelled on the exhaust stroke.
70 ✦ National DRAGSTER
                                                             the cylinder of spent gasses
                                                             but will also reduce the                      Member Track Special Programs Schedule
                                                             workload (pumping energy)
                                                             on the pistons, which frees          The NHRA member tracks listed in the calendar below will be hosting a special event on
                                                             up horsepower.                       the date listed. To schedule an event, track operators should call the NHRA Field
                                                                Though our race engines           Marketing office, 626-914-4761. For complete schedules, log on to NHRA.com.
                                                             run without second thought,
                                                             the power they create is not
                                                             free; it actually costs power to
                                                             make power. For instance,
                                                             there are losses due to
                                                             internal friction, like that
                                                             found between the rings and                         July 18                                         July 18                                         July 18
                                                             the cylinder walls, and there                  Atlanta Dragw
				
DOCUMENT INFO
Description: Starting the cycle, the piston will head down the bore. Since the piston is accelerating at great speed, it will create a pressure drop within the cylinder as compared to the pressure in the intake manifold.
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