Noob here. I get the difference between a 2 stroke and 4 stroke engine cycle, and how gas vs diesel engines work...

Noob here. I get the difference between a 2 stroke and 4 stroke engine cycle, and how gas vs diesel engines work. But how does it start? No videos show how the cycle fucking starts and it's bugging me.

>starter turns the engine over
>starts sucking in air
>fuel pump and injectors throw in fuel
>computer tells the coils to fire

I'm more interested in diesel.

So the starter is like an electric motor powered by the battery that starts turning the piston? And then as soon as the first injection gets ignited, it runs on it's own? How does RPM and different gears affect things?

Technically?
Compression is the first/last stage

Compression
Combustion
Exhaust
Intake

Exhaust can also be first.

ok, so you know how it works when the engine is running right?
the power from the bang after the suck forces the piston back down right?
ok, if you think of a stationary engine as only missing the band stroke you need to replace it with something else, this is when the starter motor/kick start/hand crank come into play, they start the whole motion at the same time powering all the auxiliaries required to get the engine to suck bang blow

Diesel?
It combusts as pressure builds.
This pushes the piston back.
Now its running on it's own.

RPM is how many cycles per minute the engine makes.
Transmission gearing;
Low gears require the engine to turn more often to make one turn of the driveshaft. This stops the engine from stalling at low speed. Higher gears lower the ratio. Overdrive gear(s) actually have the wheels turning more than the engine.

And different gears affect the speed of the cycle? How does RPM and torque and horsepower and all come into play? I know turbochargers take the exhaust and push it back into the cycle for higher compression.

>cycles
Full rotations (2 cycles for 2 stroke, 4 for 4 cycle).
My bad

2 stroke = ignition every time piston hits TDC
4 Sstroke = ignition every other time, fancy valves and shit

riden a geared bicycle?

in low gears your legs go like fuck and you go slowish, but theres less effort required to move, your energy is being converted into torque, low rpm usually equals high torque, USUALLY

in a higher gear you move faster, less turning of the pedals, but far more work is required from your leg muscles

so torque is kinda like using the lower gears to get up a steep hill, the more toque you have the greater the pulling power

>tarbos
The work by exhaust gasses spinning a turbine (like a hydroelectric dam, but with exhaust instead of water) which has a blower (like a fan) which in turn sucks in more air.
More air=more power

Air is the ICE's actual power source. Fuel is used to heat the air so that it can be used for that power. The so-called perfect ratio (stoichimetric) in gas engines is 14.7 parts air to 1 part fuel. Most gas engines run lower, while most diesels run higher.

Pistons go up and down, attached to connecting rods, attached to the crankshaft. The crankshaft turns the up/down motion of the pistons, in to a rotational motion. At the front end of the crank, there is a circular balancer, used to run accessories via belts (alt, WP, AC, etc).

On the back side (hidden by the transmission bellhousing) is a toothed wheel. On automatics, it's a flex plate, on manuals, a flywheel, but it serves the same purpose. The starter spins this wheel, rotating the engine. This rotation allows the engine to begin its' cycle.


On older gasoline cars, this begins rotating the distributor (which controls spark). The rotating action also actuates the mechanical fuel pump, feeding the carburetor.

On newer gasoline cars, engine speed is determined with camshaft/crankshaft sensors, which input rotational speed to the computer, which in turns signals the coils to fire, and the injectors to spray.

Older Diesels use mechanical injection pumps.

Newer diesels use computer controlled high pressure pumps.


As soon as the engine begins rotating, the process of combustion begins. The starter is only engaged temporarily, and as soon as the engine receives the first few power pulses (strokes), it can run and maintain itself.

How come diesel engines don't stall like gas engines? I can have a full 80,000lb load on my semi and let off the clutch and she moves on her own. I guess the bigger the engine the more compression = more torque, horsepower, etc.?

That's your torx at work.
Also, powerball.
A 700hp diesel hits it's stride at around 1500rpm
A 700hp gas hits it's stride at around 7500rpm
There's variance there, but you get my point.
Come to a stop in gear with no clutch and you'll still stall.

>powerball
Dammit google. Powerband

Its a cycle, it has no start or end.

Fucking retard.

Imagine a bike. On a single speed bike, you are limited by the rotation of your legs. However, by gearing the bike, you can pedal leisurely, and maintain a high rate of speed. The engine has a fixed maximum speed, as well as minimum, and a peak efficiency point. By having multiple gears, we can use our engine at multiple speeds, without having to compromise performance. The car can smoothly leave a stop, yet still cruise at 60mph.

Engine speed is expressed via RPM. Vehicle speed is measured in mph/kph. Like on our bike, or leg speed can remain constant, but the output of said speed (via the gears) can change. An engine can be used a 3000rpm at 15mph in first, or 70mph in fifth. However, the engine has less mechanical advantage is fifth, which is why we cannot accelerate a quickly. It's a trade off for increasing speed/usability.

What is a bull gear?

gearing plays a massive part in this, its all about inertia and momentum.
inertia is the force acting on a body at rest, torque is the value used in the auto industry for the force required to over come that inertia.
momentum is the force acting on a body in motion, so once you have a car rolling you use the torque to increase the momentum.

fuck sake mate i left school 30 odd years ago and you're making me remember physics.

Diesel engines can and do stall. The ability of a semi to pull huge loads is not some much a function of hp/tq, but gearing. In the lowest gear, operating at 2000rpm, a semi may only be able to travel 1-2mph. But the power output is multiplied by the gearing, thus the force output is much higher. This does, however, restrict the speed at which the semi can travel in that gear. Modern semis have as many as 18 speeds (gears). Keeping the engine at peak output, while having just the right gear to apply that output, is key.

Remember, engine size and compression have no correlation. a 1.8L engine can have 10:1 compression, and a 6.0L have 9:1.

Torque is a function of horsepower output, and rod length.
In laymans terms, torque is what gets you moving, horsepower is how fast you apply the torque. Not exactly how it works, but it is the simplest explanation of most real world/commonly accessible engines.

Additionally, the larger engine has an advantage in displacement, meaning the amount of air the engine can cycle through itself if one full cycle (1 rotation, 360* for a 2 stroke, 2 rotations, 720* for a 4 stroke).

The la