what is basically the function of compression ratio?

Question

w/c is better:

let's say, between 9:1 or 18:1

i saw some specs in diesel motors has 18:1
while gas has lower., which one is better?

is this also related with the fuel consumption?
does 18:1 means 18kms per 1 liter of fuel?

pls. advice

thanks

Answer 1

simple answer 120 to 170 pounds compression to fire gas properly averace is 145 if the test is done rite much more thain 175 the car pings badly as the pressure alone will ignite the fuel diecel engines dont use spark plugs they use the high compressiom aprox 400 to 500 pounds to ignite the fuel
depending on the compession reatig is how much power you will get and how much fuel you will need the stroke of the engine also plays into this a little hope this helps there is a book worth of info if you want more info you will need to resurch it out look for blue printed engines in hot rod related sorces

Answer 2

I'll try to answer your questions in simple terms, so while some of my answers won't technically be completely correct they will be for 90% of the cases you encounter. Beats bowling you over with facts and figures.

1) What is compression ratio?

Engines have pistons that move up and down, doing all the work. They move down to suck air and fuel in from the top. Then they move back up and compress that air/fuel mixture into a smaller area. Then the spark plug fires, making the fuel burn and push the piston back down hard.

The compression ratio is .. well.. the ratio that the air/fuel mixture is compressed. Say that when the piston moved down, it sucked in 200ml (or about 12 cubic inches) of air and fuel. Then when it moved back up, it compressed that air and fuel into an area only 50ml (or about 3 cubic inches) in size. The compression ratio of that engine would be 200:50 or 12:3 or 4:1

2) Diesel vs. Gas (petrol)

Diesel fuel and petrol have quite different properties, and diesel and petrol engines are designed differently. Diesel engines don't have spark plugs at all, they inject the fuel AFTER sucking in and compressing the air. They compress the air so much that it gets very hot - once the fuel is injected it burns immediately.

If a petrol engine used such a high compression ratio, the air/fuel mixture would start to burn while the piston was still moving upward and compressing the mixture. Instead of making power by pushing the piston down after it reaches the top, the engine would be working against itself.

3) Fuel consumption

Compression ratio and km's per litre are entirely different things. However, anything that makes an engine run more efficiently will improve its fuel consumption and its power output. A higher compression ratio allows you to pull more power out of that compressed mixture once it burns.

But as the compression ratio gets higher the chance of the fuel igniting while being compressed, or of it not burning smoothly (detonation, or "pinging", or "pinking") increases. Octane helps to control that - the more octane in the fuel, the more you can compress the air/fuel mix without it detonating.

That's why some high compression engines require premium fuel only. It's not about a "higher quality" or "cleaner" fuel, it's about making sure there's enough octane in the fuel to stop it detonating.

4) What's better, higher or lower compression?

The higher the compression ratio the better, until you start having problems with detonation. Engines are designed to run certain fuels, to operate in certain environments (the weather is very different in Sweden than in Saudi Arabia) .. the compression ratio is one of the many engineering decisions that go into its design.

If you want an engine that can run low-octane fuel in a hot environment, it will need to be designed with a lower compression ratio.

5) What's better, diesel or petrol engines?

Err.. what's better, spanners or screwdrivers? Depends on what you're using it for. Each has its advantages and disadvantages.

Diesel engines usually produce a tremendous amount of torque but don't like to rev. Great for a train, useless for a race car.

Answer 3

At the top of any cylinder you have a combustion chamber. The volume in this chamber to use your 18:1 ration would mean that the volume of the cylinder is 18 times greater than the volume of the combustion chamber. As the piston moves up the fuel gas mixture is compressed 18 times smaller than when it started.

The higher ratio in a diesel is because the diesel engine requires heat to ignite the fuel. As the piston compresses the fuel air mixture into the combustion chamber it causes extreme heat and thus ignites the fuel resulting in a controlled explosion and that forces the piston down. Gasoline engines require a spark for the fuel to ignite. If you were to introduce gas into a diesel engine you would get premature ignition because of the heat generated as the piston compresses the mixture.

The diesel engine is typically more fuel efficient and is used in situations and has a higher power output.

Answer 4

In math, a ratio is a comparison of two numbers.

In automotive math, a compression ratio is the comparison of the engine cylinder pressure when the piston is at the bottom (Bottom Dead Center) of the stroke, as compared to when the piston is at the top (Top Dead Center) of the stroke.

A compression ratio of 9:1 means that the piston compresses the air/fuel mixture inside the cylinder to nine times normal pressure when the piston is at the top of the compression stroke. A 9:1 compression ratio would be about average for a modern gasoline engine.

Diesel engines run on different principles than gasoline engines, and their compression ratios are higher. A ratio of 18:1 is about average for a modern diesel engine.

Answer 5

18.1 is better in a diesel because compression makes heat,and diesels make power by using heat. In a gas motor 18:1 would blow the head right off the car, WAY TOO MUCH compression. about 9:1 is common on a gas motor because gasoline is far more explosive than diesel so you cant squeeze it as tight as diesel or it will pre-ignite causing internal engine problems. Also on a diesel everything it more rigid, everything is cast iron and steel, no aluminum. Compression Ratio is how much air is in the cylinder at Bottom Dead Center compared to Top Dead Center, 9:1 means there is nine times as much room in the cylinder at BDC as there is at TDC. this is because the engine squeezes the air/fuel mixture because gas doesnt "explode" its a "rapid expansion" and it only happens when contained.

Answer 6

The 18 refers to the amount of air fuel at the bottom of the piston stroke and the one is at the top of the piston stroke. Diesel engines detonate oil under pressure and require lots of pressure to do that. Gasoline engines have to spark to burn the fuel air mixture. There are no real advandage to either system. In america diesel is used mostly for large trucks and trains.. In europe Small diesel engines with low sulfur diesel fuel are used widely. Because with a 1,600 pound car and 1.4 liter turbo diesel they get 60 miles a gallon

Answer 7

For the function that determines if the report is compressed sufficient. while the report is compressed you in addition to mght could encode interior the report a thank you to decompress the report. Your compressed report would be someplace between : no compression + 0 bytes for encoding documents, and : purely bytes for encoding + a million byte for the information you compressed. The smallest compression you are able to achieveable get for any report of length under 4 giga bytes is fullyyt a pair of bytes. this technique to decompress it would be very very massive. it would desire to be only on extensive hashmap the place each and every get right of entry to ( of say sixty 4 bits ) corresponds to a minimum of one report of length at maximum 4giga bytes. Brute tension utilized to a relatives of compression-algorithms ( the brute tension will only attempt out each and every compression algo maby various the parameters of the set of rules ) has been completed until now, its used interior the nicely usual zip application.

Answer 8

Each engine is different.

You can't compare gas and diesel engines.

Totally different.

Answer 9

google it