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# Physics/IC Engine

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Question
Question 1:
If its true that idling of automobile engine at traffic signals for short time consumes less fuel than putting it off and then starting, what is that period of time?
Question 2:
Does the amount of fuel injected into the engine cylinder only depend on acceleration pedal or also the gear. If it doesn't depend on gear, then is it not wrong to say 1st gear consumes more fuel than 5th gear?
Question 3:
Bikes exhaust sound at different pulse rate. Pulse rate is least without acceleration and increases with it. Question is does the pulse of exhaust sound same as the pulse of the engine piston strokes? If not why is the pulsating sound frequency different from 4-stroke engine cycle frequency?

Answer
Question 1 depends entirely on the engine.  There's no definitive time I can give you for that, but it is finite.  Starting an engine from rest is a wasteful process with much more incomplete burning.  Question 2 depends on the design of your fuel injection system, but lower gears definitely are less efficient than higher gears.  The third question is a little odd, I'm not sure what you mean by pulse rate.  Bikes and cars have engines with entirely different cylinder sizes and stroke rates, as well as (for some, not all) different numbers of strokes of the piston in their complete cycle.  What you hear through the exhaust is the hot gases escaping through a valve in the piston, so the number of valves also plays a role.  The question is a little vague.

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#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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