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15 votes

Is there a reason (in terms of the physics involved) why it is better to push start a car in 2nd gear rather than 1st?

It depends on the car. If it's a big displacement high performance engine, then you may not be able to get the rear wheels to turn unless you're in the highest gear. If it's got an itty bitty engine,...
  • 2,263
14 votes
Accepted

Why do some diesel engines run on diesel fuel and others on fuel oil?

Have you looked at the size of one of those maritime diesel engines? They are larger than your car and need to deliver a lot of power to move and power the ship. That takes a lot of fuel so it's ...
8 votes

How many power strokes per rotation in a 3 cylinder engine?

Each cylinder produces a power stroke for every (2-stroke engine) or every other (4-stroke engine) rotation of the crankshaft. A 3-cylinder, 4-stroke engine will produce 3 power strokes for every 2 ...
  • 6,759
8 votes

Are small car engines designed to tolerate a higher duty cycle than large car engines?

The primary issue (ignoring secondary issues like internal wear) is whether or not the engine can get rid of the waste heat. Assuming that all engines for a given fuel have roughly the same overall ...
  • 6,759
7 votes

Is there a reason (in terms of the physics involved) why it is better to push start a car in 2nd gear rather than 1st?

A higher gear ratio means that less force is needed to turn over the engine by pushing the car. Aside from the issue of the tires slipping, humans are more likely to be able to maintain the speed of ...
  • 12.5k
7 votes
Accepted

In a diesel engine, does more heat leave the engine through the tailpipe or the radiator?

They are very nearly equal for typical four-stroke non-turbo diesels under load. A turbo diesel under load should have slightly more radiator loss than exhaust loss. At the bottom is a link to the ...
  • 3,695
7 votes

Alcohol as a working fluid?

Yes - for certain applications. Low-energy, low-temperature, small installations, possibly 'accessory' power where providing a bit of weak rotary power to some point of machinery would be difficult ...
  • 6,133
6 votes
Accepted

How friction between stator and rotor is dealt with in an electric engine/motor

... there's no space between the rotor and the stator. There is always an air gap between the rotor and stator. Iron has a permeability of about 1000 times that of air so the trick for maximum ...
  • 8,794
5 votes

Why do some diesel engines run on diesel fuel and others on fuel oil?

Simple economics. Marine engines consume enormous amounts of fuel, so in order to reduce operating costs, they use the cheapest, least desirable sludge that the oil refineries can produce.
  • 6,759
5 votes

Why is soot produced in diesel exhaust, since diesel runs lean?

From the Wikipedia article: All diesel engines can be considered to be lean-burning with respect to the total volume, however the fuel and air is not well mixed before the combustion. Most of the ...
  • 3,535
5 votes
Accepted

Are small car engines designed to tolerate a higher duty cycle than large car engines?

Most (modern) small and large car engines are designed for 100% duty cycle. This means that at 100% rated power(gas pedal all the way down) the engine can run continuously. Heat dissipation is the ...
  • 7,499
5 votes

Why do some diesel engines run on diesel fuel and others on fuel oil?

A diesel engine for a car needs a fuel which is liquid even in winter. This fuel should contain a very small amount of sulfur to limit air pollution. The marine bunker oil is not liquid at room ...
  • 201
5 votes

How many power strokes per rotation in a 3 cylinder engine?

A stroke consists of either one expansion, or one contraction. As such it corresponds to half of a rotation of the shaft. In a three cylinder engine, each cylinder will stroke with 2 strokes per ...
  • 1,295
5 votes

Why doesn't the aircraft propel forward when on ground and the engine is running?

Brakes are used. And tyre wedges are also used. Turbo prop has the blades feathered to not produce any thrust. A jet is producing enough mass flow to run and little thrust.
  • 14.2k
4 votes
Accepted

Manual transmission: Why downshifting is less smooth than shifting up?

That's because when you upshift, you select a lower ratio, so your clutch speed drops. Since you took your foot of the gas, the engine rpm also dropped, and now the clutch and engine speed are close ...
  • 1,164
4 votes

Why do custom engines typically specify a type like "Ford" or "Chevy"?

There is no reason in principle why a custom engine builder couldn't cast a block themselves. Everything done by the level of automation in this process could by done by hand, given enough highly ...
  • 12.5k
3 votes

In internal combustion engines, what determines when soft or hard gaskets are used?

Gaskets are selected based upon the mating surface materials, pressure, surface area, surface condition and what they are sealing. As far as I know, harder gaskets are used in harsher locations. But ...
3 votes

What makes crosshead bearings hard to lubricate?

The crosshead bearing slides within a track and connects to the conrod and then to the crankshaft. In a vertically oriented engine the pressure on the bearing is always downwards, resulting in a ...
3 votes

Effects of center of gravity very close to rear wheels of a car

One possible reason for placing the engine and most of the weight at the back of the car would be to improve rear wheel tire friction. This would be useful if the car has a rear-wheel drive, since the ...
3 votes

How Scalable is the Wave Disk Generator Engine

"Let me say this about that" (extra points to those who recognize the originator of that phrase). First: yeah, they've invented a cool-looking device. But, they appear to be getting nowhere so far ...
3 votes

How efficient are jet engine thrust reversers?

The answer depends on factors like the bypass ratio of the engine and the design of the thrust reverser, e.g. bucket doors at the back of the engine or vanes to deflect the bypass airflow from the fan....
  • 12.5k
3 votes

Is there a reason (in terms of the physics involved) why it is better to push start a car in 2nd gear rather than 1st?

I never heard of pushing a car is 1st; have you tried it ? In the good old days when cars were not so reliable , I started more than a few in 3 rd ( of 3 speed ). Occasionally started one in second by ...
  • 5,932
3 votes

Is there a reason (in terms of the physics involved) why it is better to push start a car in 2nd gear rather than 1st?

Having pushed many cars on many occasions, on snow as well as gravel and tarmacadam. I can categorically state; on gravel 3rd best nothing lower than 2nd, on snow 4th you can try 3rd and you may be ...
3 votes

Does the turboprop engine torque get transferred to the engine mount and ultimately aircraft when engine is active?

For every action there is an equal, but opposite, reaction. Never found a case that this is not true. Torque reaction on the P51 even caused uneven tire wear: https://www.aopa.org/news-and-media/all-...
  • 14.2k
3 votes

Why is Scotch-Yoke mechanism not used for internal combustion reciprocating piston engines?

Making an engine using scotch-yoke mechanisms for all pistons on a multi-cylinder engine will increase the cost and add a lot of needless complexity and mass, especially rotating mass that won't ...
  • 14.2k
2 votes

Why do some diesel engines run on diesel fuel and others on fuel oil?

Diesel engines can run on a wide variety of fuels, as long as the fuel provides some lubrication. https://en.wikipedia.org/wiki/Fuel_oil#Uses Residual fuel oil is less useful because it is so ...
  • 133
2 votes

Limitations of the cut-off ratio in real-world diesel engines

OK, fair warning: I am answering my own question and am not a engines person. So this could be wrong. The real limit in the engine is how hot certain parts can get without breaking. This temperature ...
  • 279
2 votes
Accepted

Methods for determining Work of Diesel Engine's Isentropic Process

Your second attempt is correct, you just had two mistakes: If you re-calculated $V_1$ you'll find that it equals $0.01503$ not $0.0158$ $m^3$. same issue with $P_2$. $$P_2 = \frac{138*10^{3}*0.01503^...
  • 2,149
2 votes

Why does a radial engine need a master rod?

Having a master rod means that the bottom bearings of the connecting rods follow a fixed path throughout the cycle. If they are all attached to the crankshaft via a spider bearing it the spider ...
  • 15.1k
2 votes

Calculate pneumatic cylinder dimensions from work done

It is possible to calculate this under the assumption that all of the energy from the expansion goes into mechanical energy instead of being lost to heat transfer through the walls. In this case the ...

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