Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Turbocharging? Vacuum? Too much thinking. Smart people unite

rwhyde · 06-07-2017, 02:22 PM

Hmm, my thoughts are that turbos increase the volumetric efficiency of engines, meaning they are able to move more air into the cylinder versus a normally aspirated engine. For example purposes, if a 1.0 liter NA engine is running and atmospheric pressure is about 15 psi (14.696 really) and we ignore air friction losses, then each intake stroke the cylinder is filled with air equivalent to 15psi, that would be a 0 vacuum reading. We all know by looking at vacuum gauges, engines don't achieve that in reality due to the restrictions in the air path of the intake, and such, but for the purposes of this example, hang with me for a moment. So, for easy head math, let's say we use a turbo and boost that same engine to 15 psi, so the cylinders are not just filled with air up to zero vacuum, but then another 15 psi is added to it. That cylinder is packed with twice as much air as the original (theoretical engine), thus to keep it from running too lean and blowing up, one must supply 2X the fuel as well to achieve the same stoichiometric ratio. When if one could achieve this, then that same 1.0 liter engine is now producing significantly more power and theortically as much power as a 2.0 liter NA engine. Of course this doesn't work exactly like this in reality since if the original engine had an 9.0 to 1 compression ratio and we doubled the volume of air in the cylinder, even though the compression ratio didn't change, the actual pressure in the cylinder when the extra air is compressed is dramatically higher and the result is likely to be detonation (premature explosion of the fuel mixture if fuel is present in the mixture), if it is not using direct injection. Direct Injection, which is timing the actual presentation of the fuel into the cylinder, to allow it to compress the air and then receive the fuel. DI allows even normally aspirated engines to run higher compression ratios which produces more power, plus it uses less fuel. All good things. But nothing is free, one of the big issues with packing more air into a smaller space is those air molecules get all hot and bothered by being crammed into the small space, sort of like drivers who are all jammed together on the freeway at rush hour. So, the engine cooling system has to be able to deal with the heat to make the engine usable for everyday use. Other components are subjected to added stress as well, all of the engine bearing surfaces are not being loaded to much higher levels, placing stress on oil quality and volume, then that high pressure pump (~2500psi) required for the DI is being driven off the camshaft typically so that friction point is highly dependent on oil quality (perfection actually). So, all is not roses, but the old internal combustion engine is not dead yet, by a long shot. The last 10-15 years has seen more innovation in this power source than the previous 30 years combined. Really cool stuff is coming out of the factories every day that used to take lots of dollars and effort from "rodders" to prodcue the same power, and now they are even decently fuel efficient which is even better. Great stuff.

06-07-2017, 02:22 PM	#82 (permalink)
rwhyde EcoModding Lurker Join Date: Jul 2008 Location: Colleyville,TX Posts: 9 Thanks: 2 Thanked 4 Times in 4 Posts	Hmm, my thoughts are that turbos increase the volumetric efficiency of engines, meaning they are able to move more air into the cylinder versus a normally aspirated engine. For example purposes, if a 1.0 liter NA engine is running and atmospheric pressure is about 15 psi (14.696 really) and we ignore air friction losses, then each intake stroke the cylinder is filled with air equivalent to 15psi, that would be a 0 vacuum reading. We all know by looking at vacuum gauges, engines don't achieve that in reality due to the restrictions in the air path of the intake, and such, but for the purposes of this example, hang with me for a moment. So, for easy head math, let's say we use a turbo and boost that same engine to 15 psi, so the cylinders are not just filled with air up to zero vacuum, but then another 15 psi is added to it. That cylinder is packed with twice as much air as the original (theoretical engine), thus to keep it from running too lean and blowing up, one must supply 2X the fuel as well to achieve the same stoichiometric ratio. When if one could achieve this, then that same 1.0 liter engine is now producing significantly more power and theortically as much power as a 2.0 liter NA engine. Of course this doesn't work exactly like this in reality since if the original engine had an 9.0 to 1 compression ratio and we doubled the volume of air in the cylinder, even though the compression ratio didn't change, the actual pressure in the cylinder when the extra air is compressed is dramatically higher and the result is likely to be detonation (premature explosion of the fuel mixture if fuel is present in the mixture), if it is not using direct injection. Direct Injection, which is timing the actual presentation of the fuel into the cylinder, to allow it to compress the air and then receive the fuel. DI allows even normally aspirated engines to run higher compression ratios which produces more power, plus it uses less fuel. All good things. But nothing is free, one of the big issues with packing more air into a smaller space is those air molecules get all hot and bothered by being crammed into the small space, sort of like drivers who are all jammed together on the freeway at rush hour. So, the engine cooling system has to be able to deal with the heat to make the engine usable for everyday use. Other components are subjected to added stress as well, all of the engine bearing surfaces are not being loaded to much higher levels, placing stress on oil quality and volume, then that high pressure pump (~2500psi) required for the DI is being driven off the camshaft typically so that friction point is highly dependent on oil quality (perfection actually). So, all is not roses, but the old internal combustion engine is not dead yet, by a long shot. The last 10-15 years has seen more innovation in this power source than the previous 30 years combined. Really cool stuff is coming out of the factories every day that used to take lots of dollars and effort from "rodders" to prodcue the same power, and now they are even decently fuel efficient which is even better. Great stuff.