turbo, expansion rate, compression, cam timing, etc
turbo, expansion rate, compression, cam timing, etc
(OP)
say I raised my static comp to about 20:1. I only let the intake open 1/2 the stroke time, close about 50* BBDC so I would only have half the cyl peak pressure. and more of an expansion rate.
so with this setup will this only work with a N/A engine?
Its a given that you would need a small, fast burn chamber.
Up the compression, reduce peak pressure, and increase the expansion rate.
have the exaust open about 10* BBDC.
by creating a more complete-faster burn, and more expansion, I will have recouped any power loss from having less air.? hopefully.
also the piston wont have to use so much energy to compress the charge with the higher comp ratio.
with the greater expansion rate the egt's will lower.
(sounds great except for any kind of lean burn you will have to increase the intake temp and or use a turbo.)
so how do incorporate a turbo with this?
so with this setup will this only work with a N/A engine?
Its a given that you would need a small, fast burn chamber.
Up the compression, reduce peak pressure, and increase the expansion rate.
have the exaust open about 10* BBDC.
by creating a more complete-faster burn, and more expansion, I will have recouped any power loss from having less air.? hopefully.
also the piston wont have to use so much energy to compress the charge with the higher comp ratio.
with the greater expansion rate the egt's will lower.
(sounds great except for any kind of lean burn you will have to increase the intake temp and or use a turbo.)
so how do incorporate a turbo with this?





RE: turbo, expansion rate, compression, cam timing, etc
In order to get the same power out as with a NA engine, the turbo needs to do a lot more of the compression work (since the piston is only pumping half of its displacement and doing half of the compression). At the same time the turbine has a lot less enthalpy on hand (due to the larger expansion ratio of the piston) and possibly not enough to deliver sufficient power to the compressor wheel. It might work in a static engine rpm set up where spool time of the turbo is irrelevant.
Since turbo's are getting more efficient and the environmental laws more strict, some engines running them are actually getting 'miller cycled' just not to this extend.
Last but not least, although higher compression ratio is appealing, if one looks at the thermodynamic effciency of the ideal Otto-cycle the significant compression ratio increase from 10 to 20 will actually lead to a relatively small effciency increase of 15% (relative not absolute).
RE: turbo, expansion rate, compression, cam timing, etc
RE: turbo, expansion rate, compression, cam timing, etc
The engine rpm range will be shortened considerably, maybe making current gear ratios inappropriate.
Regards
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RE: turbo, expansion rate, compression, cam timing, etc
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: turbo, expansion rate, compression, cam timing, etc
(Obviously it would still have a lower power density than a turbo-prop engine but produce a higher power density than a conventional piston engine.)