Turbocharging? Vacuum? Too much thinking. Smart people unite

[ecocruze]

I was thinking of that from the wrong perspective apparently. Didn't take into consideration the lower compression allows more air into the cylinders. Had my pop can turbo for over a year now and it's finally making sense lol

[rwhyde]

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.

[ecocruze]

That was a lot of information. Might need a turbo to cram it in my brain lol. Appreciate you not going too brainy in the explanation. Just in the essence of ecomodding I feel I should have gone for the NA engine...maybe diesel. I have achieved over 200 miles at 60+ mpg with my 1.4t but I feel I could manage near the same numbers with EOnC with the 1.8 and engage EOC without any fear of harming a turbo. So ++ haven't really seen anyone eco drive a Cruze other than myself lol highest mpg on fuelly is near same for 1.4(minus me) and the 1.8. nevertheless it's great to be able to learn how different aspects of motors work and great to have a community here that is willing to share in Lehman's terms.
Thanks for the knowledge and glide on

Side note 48 mpg was achieved with the 1.8l Cruze with a 5 speed manual vs 6 speed of the eco which I have

[Enki]

I just found this thread from the (monthly?) email and figured I could contribute; I've not read the entire thread as there's alot to take in (more than I have time for at the moment) but as a guy who owns a turbocharged gasoline (e85 really) powered vehicle (with another being built) I figure I could add some value to the thread.

A few things to note here:

1. Turbos require a specific volume of exhaust gasses to function; a volume you won't get at cruise with anything that isn't a diesel.

2. It takes a certain amount of horsepower to sustain a constant speed; basically whatever it takes to overcome things like wind and rolling resistance and internal engine friction, etc.

3. It takes a certain amount of fuel to make that horsepower.

4 Gasoline engines do not generate boost during cruise, unless going up a steep grade. In fact, intake manifold pressure should be very, very similar to an all motor/NA vehicle.

5. Improving the thermal efficiency of the engine (less fuel per HP) doesn't really have anything to do with turbos (in fact, adding a turbo will require a fuel flow per HP increase over N/A vehicles; ex: BSFC)

6. If memory serves, fuel consumption testing is done with "typical driving scenarios" which don't include heavy throttle application; this suggests that most turbocharged engines will not see much, if any positive manifold pressure from their turbos during this testing.

Again, apologies if any of this was already covered, but if it was, it's worth reinforcing.

[ar5boosted]

ok, I think I got it now.

These modern cars such as the Toyota CH-R which are 1.2T's let you drive around in a car that basically is a 1.2 and enjoy fuel efficiency of a 1.2L car instead of the 2.0/2.4 that they should be.

When cruising they are a 1.2 so using that amount of fuel and no more.

When more power is needed, they can get the power of the 2.0 when the boost comes on.

[joemac]

Turbos also enable Miller Cycle, which is really a sort of boosted version of Atkinson Cycle. Some of the drawbacks of Atkinson Cycle operation are loss of volumetric efficiency at high BMEP and loss of low-end torque. Modern turbocharger designs do a very good job of addressing such shortcomings. A couple of current examples include the recent Miller Cycle versions of the VW EA211 1.5L and EA888B 2.0L engines. The EA211 is also using a VNT turbocharger, which helps with torque response and helps increase pressure ratio at low engine speeds.

[RustyLugNut]

You really need to separate the discussion into diesel and spark ignited engines. They respond drastically in opposite ways to turbo charging.

[ecocruze]

Lol I knew that already from some slight reading. Someone else already put some light on that in this thread as well. Interesting how they work so differently.

[freebeard]

[citation needed] Permalink #? I just got an n/a diesel, and I need to adjust the nut behind the wheel.

Although, I would prefer a 20hp altermotor to a turbo.

[Enki]

Interesting read on the Miller cycle stuff. I've basically done just that with my new engine in order to gain both more HP and better MPG; cams are redone (VVT is no longer usable on my engine due to timing differences) and the static compression ratio has been raised greatly (from 9.5:1 to 12.5:1) while actual displacement has been lowered from 2.26 to 2.0.

Good to know I was on the right track, even if I didn't know the core logic behind it.