Typically, about 25:1 for production type 4 stroke engines using diesel fuel. Materials, and thus costs, are probably the main limitation. Emissions are another factor, NOx goes up with compression ratio.

 up to hundreds of bar

It depends on the degree of supercharging. Naturally aspirated diesel engines in automotive, truck or commercial vehicle applications have compression ratios of up to 25:1 as mentioned by Robert. Turbo- or Supercharged diesel engines have lower compression ratios, e.g. 14:1 to 20:1 depending on the intake air pressure. Supercharging grades of 1.5-3 and even more are reached in common in diesel engine applications. 

Kind regards,

Mario

All compression ignition engine products today are supercharged diesel engines. For this reason they have 14:1 to 18:1 compression ratios, with the maximum intake manifold pressure equal to 2,5 - 2,8.

Francesco  

Dear Andras

Compression ratio is defined as the ratio when total cylinder volume when piston is at its bottom dead center divided by the clearance volume( volume of cylinder when piston is at its top dead center and so it has no units i.e. dimensionless.

as per my knowledge 25 is the maximum compression ratio achieved by some of the diesel engines....

Please specify the manufacturer of the engine that has a compression ratio of 25 ?

This range is from literature, I think from retired commercial naturally aspirated diesel engines. Examples of modern commercial diesel engines with high compression ratio:

Hatz (compression ratio 22): http://www.hatz-diesel.com/en/products/diesel-engines/b-series/product/details/name/1b20/

Kohler (compressioon ratio 22.8): http://www.kohlerengines.com/onlinecatalog/productDetail.htm?productNumber=KDW702

Kind regards,

Mario

Dr Sharma  do you have a manufacturer in mind who manufactured an engine with a compression ratio of 25? Please give some details

- Here is an additional link, which might be of interest for you:

http://russianpatents.com/patent/249/2491429.html

- Exemplary diesel engines with high compression ratio up to 24:

http://www.jc-swan.com/english/products.asp?Action=Detail&ID=195&ClassID=97

http://www.jc-swan.com/english/products.asp?Action=Detail&ID=173&ClassID=94

kind regards,

Mario

Thank you Mario

They only have 2 kW engines with compression ratio of 23 which is a very small engine.

Yes, these high compression ratios mainly occur in small diesel engines today. Most of them are for mobile industrial applications, e.g. generators or water pumps. Development targets are a certain power output, even if the engine displacement is small, and (relatively) low fuel consumption - and this with low cost technologies. 

Kind regards,

Mario

What is the normal compression ration for single cylinder diesel (Trem III A Emission ). whats is the port timing diagram for the same in real time application.

what will be the consequences in increasing CR apart from higher nox emissions

what are the limitations in increasing CR

Temperatures in the combustion chamber will rise to higher limits that may not be tolerated by the materials surrounding the combustion chamber. Expansion or even melting and then jamming of piston may occur resulting in complete mechanical failure.

Dear Kamal Nasreldin Abdalla,

I think its maximum 25:1.

For a temperature concern I am agree with you in a totality. (However, in most real-life internal combustion engines, the ratio of specific heats changes with temperature and that significant deviations from adiabatic behavior will occur).

Compression ratios are often between 14:1 and 23:1 for direct injection diesel engines, and between 18:1 and 23:1 for indirect injection diesel engines. Since diesel engines operate on the principle of compression ignition, a fuel which resists auto-ignition will cause late ignition, which can lead to engine knock. Anything over 10:1 is a high compression ratio. Anything over 12:1 is "highly compressed".

PSi limitations

Today, the average high-performance street or strip turbocharged four-cylinder race engine sports a compression ratio of 9.5:1, with some even running compression ratios as high as 11.5:1 or more on alcohol. Modern automobile technology allows our racing generation to get the best of both worlds. Boost levels above 12 psi should generally be avoided even with racing fuel on a 9.5:1 motor. Compression ratios of 10:1 and higher require lower boost levels, higher octane fuel, inter cooling, or some combination of the above. Compression ratios in the 7 or 8:1 range can usually handle 12-20 psi on pump gasoline.

Air is compressed much more highly during the succeeding compression stroke than would be the case with a spark-ignition engine, with compression ratios of up to 25:1 typical. When the piston is at the highest point within the cylinder, that's called Top Dead Center, and that's where cylinder volume is smallest. The comparison of these two volumes is where your ratio comes from. Increase the compression ratio: Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (before the spark plug ignites it). Higher-octane gasolines prevent this sort of early combustion.

Automotive engineers constantly trying improve fuel efficiency and fuel economy by designing new efficient engines with high compression ratios. The higher the ratio, the more compressed the air in the cylinder is. ... It's the same thing with compression ratios. By keeping the explosion in a smaller space, more of its power can be harnessed. Increase in compression ratio induces greater turning effect on the cylinder crank. That means that the engine is. Getting more push on the piston, and hence more torque is generated. The torque gain due to compression ratio.

A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air–fuel mixture due to its higher thermal efficiency. This occurs because internal combustion engines are heat engines, and higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature. Since diesel engines operate on the principle of compression ignition, a fuel which resists autoignition will cause late ignition, which can lead to engine knock. Diesel engines have a higher peak combustion temperature than petrol engines, but the greater expansion means they reject less heat in their cooler exhaust. However, in most real-life internal combustion engines, the ratio of specific heats changes with temperature and that significant deviations from adiabatic behavior will occur.

Compression pressures that are too high can result in difficult starting and detonation or “pinging” which in turn can cause engine damage. If the static compression pressure is too high or too low, the engine will not run as well as it should, and in some cases the resulting problems can be serious. Temperature rising must be considered as it is also a serious matter in this concern.

Hope it help you out.

Ashish

Generally the range of compression ratio starts from (12-24):1