30th December 2005, 22:49 | #16 | |
BHPian Join Date: Dec 2005 Location: Jacksonville, FL
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There were several two stroke cars (some french manufacturers i think) that were quite popular in racing cos of their awesome power to engine weight ratio... theoretically, the biggest advantage with 2 strokes is power on every alternate stroke and lesser moving parts.. Heh heh. And anyone who doubts the power outputs of a 2 stoke engine has obviously never ridden a properly tuned 2-stroke monster Anyone try getting their hands on Rossi's favorite bike (which happens to be a 2-stroke 500 cc monster)... | |
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8th January 2006, 00:18 | #17 | |
BHPian Join Date: Dec 2005 Location: SINGAPORE
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Please read the thread started by GTO - Most powerful diesel engine in the world. It is a two stroke engine and it has one of the highest thermal efficiencies in the world. Please note that supercharging (turbocharging is one form of supercharging) is used to increase the power of the engine while keeping the displacement same. Theoritically, it has got nothing to do with thermal efficiency. So what is the problem? The main problem is the lubrication of gudgeon pin. The lubrication of gudgeon pin is not purely hydro-dyanamic but more so of boundary layer lubrication. In 4-stroke engines, while the suction stroke is taking place, the load on gudgeon pin is reversed or is minimum. The lubricating oil has a chance to fill up the top space of gudgeon pin. In 2-stroke engines, the load on gudgeon pin is never reversed, so their is no chance of oil to reach the top space of gudgeon pin and hence gudgeon pin bearing is liable to fail. In large engines, the one described in above mentioned thread, separate gudgeon pin in form of crosshead. These are made large to increase the area under lubrication and hence reduce the bearing load. Also there is a provision of special supply of lubricating oil under pressure to the top of crosshead. But becuse of their size they are not suitable for cars. They are mainly used in shore specialised powerplants etc. | |
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8th January 2006, 10:38 | #18 | ||
BHPian Join Date: Dec 2005 Location: Omnipresent
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And this scenario threw two more questions, 1) Though it is proved that a 2S diesel engine is much compact, provides better power/unit voulme, highly efficient, why is it that the conventional diesel engines are 4S? 2) Why petrol engines cant employ same injection principle? And about the type of luburication you specified, just read this post Quote:
And one more thing, before I thought turbocharging/supercharging will increase compression ratio, but just now I recalled that turbo/super only increases the cylinder pressure, not the compression ratio (the displacement is constant), in fact the turbo engines have relatively lower compression ratio...OOPS!! But still new questions aroused and remains unsolved!!! Please reply!!! Pratheesh Prakash Last edited by pratheesh : 8th January 2006 at 10:41. | ||
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9th January 2006, 00:33 | #19 | ||||
BHPian Join Date: Dec 2005 Location: SINGAPORE
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Thermal efficiency depends on lot of other factors and two stroke or four stroke plays a less important role. People were happy with around 45 % thermal efficiencies (car engines thermal efficiencies were much lower - in 90s they were able to get more that 30 %) till the Israel-Egypt war created an oil price shock and research for higher thermal efficiencies started. All these factors are mainly dependant upon the economic factors. You can see that in India also. Suddenly there are more diesel variants in the market and Honda city has also developed I-DSi engine. Fuel loss etc are tolerated when leagal system allows, combined with the affordability of fuel cost. People who increase power of their vehicle engines to extremes are not bothered by fuel loss - their vehicle thermal efficiency is lower than the stock car engines. Please note that fuel loss is dependant on how the fuel is burnt and more of less independant of how the fuel is injected. You would have noted the two numbers of spark plug in Honda I-DSi engine to reduce fuel loss - and it is a four stroke engine. Also please note that in diesel engines, fuel is injected near the end of compression stroke and injection is comleted during expansion stroke. If beginning of fuel injection is during expansion stroke, there won't be enough time to burn the fuel completely and you may find the flame coming out of the exhaust valves which will get burnt out in no time (metallurgical limitations) Quote:
2) Petrol engines can employ same injection principles, but it means that same kind of high pressure fuel pump and high pressure injectors, which means the increase in cost by a huge amount without giving any significant advantage - and I think no body is going to pay for that just for fashion which nobody can see!!! Quote:
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RK | ||||
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9th January 2006, 00:43 | #20 |
BHPian Join Date: Dec 2005 Location: Mumbai
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| Hey Goldie i do agree with you earlier i had pulser but sold it as it was not fun to ride n now i ride a YAMAHA RX100 its an 1988 model its 17yrs old n still has the power n very low on maintenance today also i can beat a ZMA n P180 on the road on innitial pickup i just LOVE my bike |
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