Internal Combustion Engine

This is an engine which harnesses power from a fuel by a combustion process
inside the engine itself. There are many different types, however, for the sake of
automotive purposes, there is only one of interest- the 4 stroke piston engine.
This engine typically burns gasoline, however, there are some diesel powered
automotive models. All modern automotive combustion engines in mass production
are fuel injected rather than carbureted because fuel injection is much more efficient.

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A 4 stroke (or 4 cycle) engine is named so because it has 4 distinct phases of
operation- intake, compression, ignition, and exhaust. These occur in the same
order every time and require 2 full revolutions of the crankshaft or 4 piston strokes
to complete (down, up, down, up). Each stroke of the piston equates to a half turn
of the crankshaft. The piston slides up and down in the cylinder in a reciprocal
fashion and is connected to an offset journal on the crankshaft via a connecting
rod. The main job of the crankshaft is to turn the piston's reciprocal motion into
rotary motion. At the end of the crankshaft sits the flywheel. The flywheel is heavy
and its job is to use its large momentum to continue the crankshaft's revolution
through the non-power cycles.

The valve train is complex, can vary, and thus earns its own paragraph. Basically
the valve train is a term to describe all of the parts including the valves and
components which open them. Operation of the valves originates from the properly
timed rotation of a camshaft. The camshaft is mounted parallel to the crankshaft
and its purpose is to open the right valves at the right time. It is turned at exactly half the speed as the crankshaft and is turned by the crankshaft by meshing gears, timing belts, or timing chains. The camshaft has eccentric lobes on it
and when the peak of a lobe forces either on the valve directly or indirectly
through a lifter, the valve opens. After the peak of the lobe on the camshaft rotates
away from the valve or lifter, the valve is closed by a heavy spring attached to it.Where the camshaft is located can vary. Typically, it is located in the crankcase.
On an ICE where the cylinders form a V, it is directly above the crankshaft in
the saddle of the V. On a single or inline cylinder block, it is above and offset to
the left or right of the crankshaft. If the camshaft is in the crank case, it will
force up on a lifter, which forces up on a pushrod, which forces up on one side
of a rocker. Rockers look like see-saws with a fulcrum in the middle. When the
pushrod forces up on the input side, the output side forces down on the valve.
Racing cars and and many modern automotive engines now use an OHC (overhead
cam). In this configuration, the cam is located above the cylinder head and the
lobes on the camshaft force down on the valves directly. Some engines with an
OHC only have one camshaft operating both intake and exhuast valves (SOHC)
while others have two camshafts; each dedicated to either the exhaust valves
or the intake valves (DOHC). OHC configurations are perform better at higher
speeds because they open valves much quicker due to their direct interaction
with the valves.]

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Although I will not get into the grit of the automotive computers here, fuel
injection and TCI (transistor controlled ignition) need to be covered. TCI basically
means the ignition timing is controlled by an EMM (electronic managment module)
or a PCM (powertrain control module). The EMM or PCM are both types of computers
and recieve information on which they base fuel management and ignition time through
electronic sensors. When the computer senses it is time to ignite a cylinder, it makes
a spark jump across the electrodes of the spark plug in the cylinder by emitting
a brief low voltage current through a series of wire coils which induce a high voltage
current to the spark plug. The computer times fuel delivery to the combustion
chamber in much the same way by emitting a low voltage pulse to a fuel injector.
Fuel is kept in a pressurized rail at around 40psi and when the injector recieves a
current, its soleniod controlled valve opens and the pressure of the fuel behind it
forces a spray of fuel through the open soleniod valve opening. The computer can
put more fuel in the engine by allowing the injector to stay open longer and visa
versa. Fuel injectors can be located in the intake manifold and act much like a carburetor, mixing fuel with the intake air stream, or they can be placed directly
in the cylinder and inject fuel just before the ignition stroke. The latter placement
of the fuel injectors is called direct injection. 402px-Fuelinjector.png

Lubrication is necessary in an ICE to lubricate moving parts, clean them, keep them
cool, and to protect them from corrosion. All modern automotive engines use apressurized lubrication system in which an oil pump is driven by the engine to pump
oil through orifices, groves, and jets to deliver the oil where it needs to go in
the engine. In addition to lubrication systems, all ICEs must have a cooling system
or they will overheat. A very few automobiles are air cooled by a fan driven by the engine blowing air across cooling fins cast around the cylinders. The vast majority
are liquid cooled with some concentration of antifreeze and water pumped around
the cylinders by an engine driven pump. Some of hot cooling solution is routed to
the heater core in the climate control assembly then to the water pump but most
travels past the thermostat to the water pump if the thermostat is open. The thermostat keeps most of the coolant from circulating through the engine if it is
below ideal operating temperature. An ICE running too cold will cause a large build
ups of carbon to form in the engine which ironically will cause it to overheat as
well as cause premature physical wear of the moving parts. If the thermostat is
closed, coolant will circulate between the radiator and water pump. A small amount
will continue to circulate through the engine via the heater core. If the thermostat
is open, the coolant will circulate from the engine through the thermostat, water
pump, radiator and then end up back in the engine. The antifreeze keeps
the cooling water from freezing and cracking the block as well as keeping the water
from boiling and producing steam if the engine temperature only rises slightly above
212F.
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At the start of the intake stroke, the piston is at TDC (top dead center or at the
highest point of its travel). It has just completed forcing out the exhaust gases.
The exhaust valve is open and the intake valve will open. Both intake and exhaust valves will stay open for a crucial time period just after TDC called valve overlap.
Valve overlap is necessary because as the piston moves downward, it creates a
vacuum which draws in the intake air or air fuel mix. The incoming air forces out the
remaining exhaust and the exhaust valve then closes. (The reason why exhaust
gases are not drawn back in valve overlap is that the intake valve is larger,
provides less resistance to the equalizing pressure, and thus allows the the intake
air rushing in to equalize the vaccuum to overpower the exhaust.) As the piston
continues downward in the intake stroke, more intake air or air/fuel is drawn in.
At BDC (bottom dead center or the bottom of the piston travel) the intake valve
closes and thus the intake phase of the engine is complete.

The compression stroke continues after the intake. This stroke is necessary
because the key to combustion power in an ICE is the fact that the fuel vapors
are compressed together. They are more volitile in this state. Typically, and ICE
needs to compress the air/fuel mix to at least 90psi to get a sufficient combustion.
As the piston moves up from BDC in the compression stroke, both the intake and
exhaust valves are closed. The closer the piston gets to TDC, the more
compressed the air/fuel mix gets because the volume of the cylinder is diminishing. Depending on ignition timing, the compression stroke will end at a definite point
around TDC.

The ignition, or power stroke can begin anywhere from a few degrees BTDC
(before top dead center) to several degrees ATDC (after top dead center). If
the engine is turning fast, ignition will come BTDC because fuel does not
combust instantaneously and it requires time after ignition to combust. The fuel
always combusts just past TDC on the piston stroke. If the engine is turning slower,
ignition starts a little after TDC so that the fuel combusts at the right time. At any rate, when the ignition source (ie the sparkplug) ignites the air/fuel mix, the mix
explodes creating a forceful expansion of exhaust gases which forces the piston down.
This part of the ignition stroke is what powers the engine and makes it turn on its
own after it is started. After the piston has reached BDC on the ignition stroke, the ignition stroke is over and the exhause stroke begins.

The exhaust stroke's only purpose is to evacuate spent fuel from the cylinder
so a fresh charge may be brought in. At the start of the exhaust stroke, at
BDC, the exhaust valve opens and the piston moves up which forces all of the
exhaust out except for what remains at the top of the combustion chamber. (This
small amount of exhaust will be evacuated by valve overlap in the intake stroke.) At TDC, the exhaust stroke ends and the intake stroke begins again.

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