36 votes
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How does turning off electric appliances save energy

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is ...
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19 votes

How does turning off electric appliances save energy

Timescales on the grid Power demand fluctations can be broken into timescales from micro-seconds to decades. On the "decades" end of the scale, the power industry and utility regulators work ...
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  • 402
18 votes

How can "mpg" be high under low engine load?

Thermodynamic efficiency vs. fuel economy When you cite an efficiency of 25-30% for an internal combustion energy, you're talking about the thermodynamic efficiency of the engine. This is, at the ...
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12 votes
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Why wont Petrol engine run on Acetylene?

There are certainly a few reasons why acetylene is not a very practical fuel for an IC engine. Perhaps the most important is that it is inherently unstable and tends to explode under pressure, this ...
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10 votes

How does turning off electric appliances save energy

Yes, they monitor demand and due to differences in how different power stations are controlled they can increase or reduce output to match demand. Some power plants like nuclear run at full output as ...
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7 votes
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While going downhill, does my car consume less fuel when in neutral or in gear?

Note: This is specific to gasoline based engines. Assuming your car was produced after the ~1990's it is equipped with a Deceleration Fuel Cut-Off (DFCO) system which cuts the fuel flow to the ...
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6 votes

How can "mpg" be high under low engine load?

The plot in the question does not apply to the situation being asked. The power capacity of an automotive engine is dynamically changed while driving by both altering the RPM and by throttling the ...
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  • 269
6 votes

How does turning off electric appliances save energy

Peak Demand One of the biggest issues in the electricity business is managing peak demand. This is the maximum amount of electricity needed at any one time. Typically this will be the middle of the ...
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5 votes

Which is fuel efficient, roadways transport vs waterways transport?

Unfortunately, this question shares multiple similarties to the phrase "How long is a fish?"; meaning that the answer is very dependent on the assumptions, limitations and scope of your ...
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  • 148
5 votes
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What does MM prefix mean in MMtoe?

TL;DR: the MM in MMtoe is probably related to the Latin Numeral M (for 1000). In that context MM means one thousand thousands (i.e. one million) Although this is very confusing, the bottom line is ...
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5 votes

How does the optimal-gear indicator work?

In a modern car with electronic engine control, fuel injection, etc, the amount of engine power is always dependent on what the ECU is doing in response to the driver's control inputs like throttle ...
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4 votes
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How much air will an engine use per tank of gas?

You probably want to look at stochiometric ratios by mass. However this is a difficult problem to solve from first principals as for an IC engine air is essentially free and monitoring its ...
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4 votes

While going downhill, does my car consume less fuel when in neutral or in gear?

The answer depends a great deal on the control system around the engine, and how fast you are going down the hill relative to the gear you are in. For a basic engine system, like 1960s or earlier, at ...
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3 votes

Does the shape of a car really matter for how much gasoline it drinks?

The difference is in the drag coefficient. Typical drag coefficient of the 50's cars have been in the range of 0.38 to 0.42 or so. typical drag coefficient of modern cars even the ones not renowned ...
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3 votes
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does payload weight distribution affect rolling resistance?

Consider to simplify the model to two wheels in line as in a bicycle. For nice round figures, the tires are inflated to 100 pounds per square inch. The load is two hundred pounds and is placed over ...
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3 votes

How can "mpg" be high under low engine load?

Petrol engines have a very poor efficiency at low load... no ifs or buts. The 34mpg efficiency is not quoted at low load. There is an ideal speed at which maximum mileage occurs... engine efficiency ...
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3 votes

How can "mpg" be high under low engine load?

I know it's an old thread, but I can't resist taking a stab at it. Especially when there's so much bad or unrelated info in the other answers. Thermal efficiency and fuel mileage ARE related - there ...
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3 votes

How can "mpg" be high under low engine load?

I can give you an analogy: For a DC electric motor, efficiency is highest at a point LESS THAN its maximum rated power. The loss mechanisms are friction from fast rotation, and magnetic core losses ...
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  • 209
2 votes

How can "mpg" be high under low engine load?

Rephrasing your question: 1. How much energy does a car use at 60mph doing 34mpg? 2. What is its efficiency if it requires 20hp to maintain constant speed? In SI units: Car at 26.8m/s doing 14.4km/L ...
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2 votes

How can "mpg" be high under low engine load?

Bear in in mind that the chart shown relates to the thermal efficiency of the engine alone and doesn't consider a moving car as a complete system and also that the vertical axis appears to be labeled ...
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2 votes

seperate engines working vs single engine

In your scenarios, there are two places that the energy ends up: as kinetic energy in the vehicles themselves (0.5 × mass × velocity squared) and as losses (rolling resistance, air ...
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2 votes
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Which is fuel efficient, roadways transport vs waterways transport?

From the European Environment Agency - Rail and Waterborne cited in Jon Arnt's answer: Chart shows gm CO2 / tonne km. For my preceived interpretation of the question. The best way to ship cargo on ...
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2 votes
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How to Calculate Approximate Fuel Consumption from Engine Specs

In short, it's complicated. In long: What you tried is the cylinder volume times revolutions per minute. Indeed, this gives the per minute volume of air-fuel mix entering each cylinder of the engine. ...
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  • 148
1 vote

Where can I find efficiency metrics for diesel engines?

Some engine manufacturers use BSFC which is the fuel consumption compared to the power produced. As you know the engines you want to look at you should be able to get the figures.
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1 vote

Can we currently achieve 55 MPG on Non-Hybrid vehicles using internal combustion engines?

It's more than possible. The 2020 Toyota Prius already claims it with 58 on the highway and 56 combined highway and city. The limit is higher. Here is an article that covers a lot of details
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1 vote

Can turbine engines really run on "just about anything"?

Your range of "gasoline to sunflower oil" (in a comment) is too small. Turbine engines run very well on natural gas, when used for gas pumping applications. Combustion is continuous, so auto-...
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1 vote

Whats the purpose of a main metering system in a carburetor?

IF I understand your question, you're asking why we need a main metering system with any moving parts. It sounds like your assumption is that, as the throttle is opened, the increased airflow should ...
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  • 21
1 vote
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Best fuel for supercar engines

Use the fuel specified by the manufacturer in the car's manual and/or near the gas cap. Likely a High Octane Fuel based on your question. If you're referring to Octane levels... The higher the Octane,...
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1 vote

Why wont Petrol engine run on Acetylene?

Due to the dangers involved with storing and transporting compressed or liquid acetylene, you would probably have to make use of an onboard acetylene generator, fueled with calcium carbide. Acetylene ...
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1 vote

How can "mpg" be high under low engine load?

That chart is suspect. If you look at the Web page it was taken from, it is clear that the author of that page does not understand the basic terms that he is using, like "load", "power", "torque", ...
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