how fast does a piston move inside the cylinder?

Question

if the car maxes out at around 120 mph how fast would the pistons be moving is it possible for the pistons to move so fast that they break the sound barrier? does engine size really matter in terms of piston speed how would a V12 differ from a V8 and V10 or a V6. and do the same rules apply to a rotary engine like the ones on RX8s?

Answer 1

This is an interesting question. Lets say that a car running at 120mph has its engine turning 6000rpm. It doesn't matter if its a v-8 or a v-12, its turning 6000 rpm. Lets assume a 4inch stroke. For every revoltion the piston makes one full trip in the cylinder or a total distance traveled of 8 inches. At 6000rpm the piston would make 6000 8 inch trips or 48000 inches in 1 minute. If we divide 48000 by 60 (seconds) we get 800 inches a second and if we divide that by 12 (inches in a foot) we get a total of 66.666 feet per second. So a piston with a 4inch stroke turning in an engine at 6000 rpm travels at 66.666 FPS. (if I did the math right) A rotary is different since it has no actual pistons and is in fact spinning and not reciprocating.

Answer 2

Well first of all the piston is going to be doing the same thing the rod journal on the crank is and thats measured in RPM's. Now for a rotary motor the "wankel" or rather the triangular peice that acts as the multi-surfaced piston rotates or for a better word oscalates at a different kind of speed. Which in many cases is not the same RPM's as a piston. The wankel spins and dosnt really have much of a critical point like piston motors do which just goes up and down. Thats why you can rev the crap out of a rotary motor without messing anything up really. If anything in the critical area of a rotary motor to worry about is the apex seal going out while at those upper RPM's. Apiston motor you would just throw a rod or worst.

Answer 3

A passenger car engine pistons move at about 50 feet per second at high rpm. A high revving sports car might be 75. A race car maybe 100. Formula one cars can hit an astounding 130. Nowhere near the speed of sound, 1000 feet per second.

The problem with high piston speed is the enormous force required to decelerate the piston and reverse its' direction at the ends of the stroke. That makes huge demands on bearings and crankshafts.

The number of cylinders counts because more cylinders let you run a shorter stroke which reduces piston speed. And use more and lighter pistons which reduces the force needed to change their direction.

You don't have to reverse the direction of a rotary engine. The limiting factor here for high rpm is wear on the edge seals.

Here's a piston speed calculator:

http://www.csgnetwork.com/pistonspeedcalc.html

Answer 4

I went back a few years to a Ford Hi Performance 289 engine because I know the specifications by heart. The engine is similar to the Ford 302 and 5.0 Liter engines.

The 289 had a stroke of 2.87 inches and develops 271 horsepower at 6,000 RPM. That 2.87 stroke means it travels 5.74 inches with each revolution. That multiplied by 6,000 RPM will give you 34,440 inches per minute. Divide by 12 gives use 2,870 feet per minute. That multiplied by 60 minutes equals 172,200 feet per hour. That divided by 5,280 equals 32.613636 miles per hour.

So there you are a 2.87 inch stroke at 6000 RPM is 32.613636 Miles Per Hour. That is assuming I didn't screw something up. And that has happened to me before but I did these calculations three times so I am fairly confident.

Since the speed of sound is well above 600 MPH there is no danger that piston will go supersonic anytime soon.

As far as other engines go, you will have to run the numbers yourself. You need to know the stroke and the RPM they will be operated at. I don't know the answer to this but it wouldn't surprise me if most engines operated at a very similar piston speed. I can't tell you why I feel that way, it's just something in my gut talking to me.

And when we talk rotary, all bets are off. That engine is nothing like a piston engine and it takes someone better at this than I am to explain it properly.

Answer 5

Piston Speed Calculator

Answer 6

In order to calculate the piston speed, you need to know the rpm of the engine and the stroke length.
Parameters for piston engines do not apply to rotaries.

Answer 7

it all depends on the engine size (displacment)
went through college a couple years ago, and without digging up my books, i think the max speed the pistons move (mass, gravity, strengh) is around 20 meter/ second (the whole engine)

rotary engines work different, the can run faster since they have less moving parts compared to a regular engine

Answer 8

one way of including warmth to a substance is to position it in contact with a hotter substance: the hotter elements molecules flow swifter than your cool substance ( that is the way you recognize it truly is hotter ) so on the junction between the nice and comfortable merchandise and your cool merchandise quick paced molecules bang into slower shifting ones and speed them up at the same time as slowing down themselves. Then there are a best purchase of outcomes that contain molecules or crystal lattices being exited by technique of certain phonon frequencies for radiative move yet those are a lot less intuitively feasible.

Answer 9

I didn't know the rotary (Wankel) engine was still in production.

Breaking the sound barrier? Warp 5 Mr. Sulu!

Answer 10

The internal combustion engine is an engine in which the burning of a fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand. The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself.
All internal combustion engines must have a means of ignition to promote combustion. Most engines use either an electrical or a compression heating ignition system. Electrical ignition systems generally rely on a lead-acid battery and an induction coil to provide a high voltage electrical spark to ignite the air-fuel mix in the engine's cylinders. This battery can be recharged during operation using an electricity-generating device, such as an alternator, driven by the engine. Compression heating ignition systems, such as diesel engines and HCCI engines, rely on the heat created in the air by compression in the engine's cylinders to ignite the fuel.

Once successfully ignited and burnt, the combustion products, hot gases, have more available energy than the original compressed fuel/air mixture (which had higher chemical energy). The available energy is manifested as high temperature and pressure which can be translated into work by the engine. In a reciprocating engine, the high pressure product gases inside the cylinders drive the engine's pistons.

Once the available energy has been removed the remaining hot gases are vented (often by opening a valve or exposing the exhaust outlet) and this allows the piston to return to its previous position (Top Dead Center - TDC). The piston can then proceed to the next phase of its cycle, which varies between engines. Any heat not translated into work is normally considered a waste product, and is removed from the engine either by an air or liquid cooling system.
The Otto cycle is characterized by four strokes, or straight movements alternately, back and forth, of a piston inside a cylinder:

intake (induction) stroke
compression stroke
power (combustion) stroke
exhaust stroke
The cycle begins at top dead centre (TDC), when the piston is furthest away from the crankshaft. On the first stroke (intake) of the piston, a mixture of fuel and air is drawn into the cylinder through the intake (inlet) port. The intake (inlet) valve (or valves) then close(s) and the following stroke (compression) compresses the fuel-air mixture.


Four-stroke cycle (or Otto cycle)The air-fuel mixture is then ignited, usually by a spark plug for a gasoline or Otto cycle engine or by the heat and pressure of compression for a Diesel cycle or compression ignition engine, at approximately the top of the compression stroke. The resulting expansion of burning gases then forces the piston downward for the third stroke (power) and the fourth and final stroke (exhaust) evacuates the spent exhaust gases from the cylinder past the then-open exhaust valve or valves, through the exhaust port.
The amount of power generated by a four-stroke engine is ultimately limited by piston speed, due to material strength. Since pistons and connecting rods are accelerated and decelerated very quickly, the materials used must be strong enough to withstand these forces. Both physical breakage and piston ring flutter can occur, resulting in power loss or even engine destruction. Piston ring flutter occurs when the piston rings change direction so quickly that they are forced from their seat on the ring land and the cylinder walls, resulting in a loss of cylinder sealing and power as well as possible breakage of the ring.

One important factor in engine design is the rod/stroke ratio. Rod/stroke ratio is the ratio of the length of the connecting rod to the length of the crankshaft's stroke. An increase in the rod/stroke ratio (a longer rod, shorter stroke, or both,) results in a decrease in piston speed. However, again due to strength and size concerns, there is a limit to how long a rod can be in relation to the stroke. A longer rod (and consequently, higher rod/stroke ratio,) can potentially create more power, due to the fact that with a longer connecting rod, more force from the piston is delivered tangentially to the crankshafts rotation, delivering more torque. A shorter rod/stroke ratio creates higher piston speeds, but this can be beneficial depending on other engine characteristics. Increased piston speeds can create tumble or swirl within the cylinder and reduce detonation. Increased piston speeds can also draw fuel/air mix into the cylinder more quickly through a larger intake runner, promoting good cylinder filling.

An engine where the bore dimension is larger than the stroke is commonly known as an oversquare engine, and such engines have the ability to attain higher RPM. Conversely, an engine with a bore that is smaller than its stroke is an undersquare engine. Respectively, it cannot attain as many RPM, but is liable to make more torque at lower RPM. In addition, an engine with a bore and stroke that are the same is referred to as a square engine.
The bullwhip or stockwhip was probably the first human-made object to move faster than sound. The tip of the whip breaks the sound barrier and causes a sharp crack--literally a sonic boom. Many forms of ammunition also achieve supersonic speeds.

The tip of the propeller on many early aircraft may reach supersonic speeds, producing a noticeable buzz that differentiates such aircraft. This is particularly noticeable on the Stearman, and noticeable on the T-6 Texan when it enters a sharp-breaking turn. Note that this is in fact undesirable as the transonic air movement creates disruptive shock waves and turbulence.

The sound barrier was first broken in a vehicle in a sustained way on land in 1948 by a rocket-powered test vehicle at Muroc Air Force Base (now Edwards AFB) in California. It was powered by 6000 pounds of thrust, reaching 1,019 mph
passenger cars have a max RPM of abput 6 or 7000, it doesn't appear that it could be done in a stock vehicle.