Current Peak Cylinder Pressures on Turbo S-I engines

[TrackRat]

I have read a number of threads here regarding PCP on turbocharged engines, mostly in regard to Diesel or other experimental or developing engine tech. The minimal info. on turbo S-I PCPs however left me wanting for more info. Since virtually all major pass car companies are downsizing to turbo 4 & 6 cyl. engines for EPA mandated mpg requirements in the U.S., I thought this might be a good time to revisit this subject as the prior threads were circa 2008 and a lot of changes have occurred in pass car turbo engine development since then.

My personal interest is for a turbo 3.2L VR6 engine project where I want to be certain that the head gasket is capable of managing the PCP under maximum boost even though this would only be encountered for short duration at WOT. I've reviewed many SAE and other tech papers on theoretical / modeling techniques to estimate PCP but the best real world measured hard data I have found was on the Honda turbo 1.6L F1 racing engine circa 2000. The PCP on this engine was 16.7 MPA, i.e. ~2422 PSI @ 2.5 bar absolute(A), boost @ 12,000 RPM. I will be running a max of 2.38 bar (A) (on rare occasion), at a more modest 6,500 rpm. The PCP is likely to be some what limited by the 92 R+M/2 premium pump octane fuel used based on my past experience. Honda's 1.6L turbo F1 engine like other F1 engines of the day used 84% Toluene with higher energy content but more importantly the ability to use 37 degrees total advance at ~12,000 rpm while only measuring 101.7 RON. (The F1 rules limited the fuel octane to 102 RON). I have dyno developed numerous turbo S-I engines with <2 bar (A) boost on Indolene (simulated 92 R+M/2 premium fuel), that limited max ignition advance to ~20 deg. total @ WOT in the RPM range from ~4500-6500 rpm.

On a four cyl. turbo S-I pass car engine circa 1990 that I worked on we were seeing ~1250 PSI measured PCP in this engine with ~2 bar (A) boost. Based on that engine I'm estimating the 3.2L VR6 engine to have ~1724 PSI PCP at the increased 2.38 bar (A) boost. I know GM, Ford, VW and many more companies are currently running some significant boost in small turbo S-I pass car engines so I'm hoping that those with firsthand knowledge can offer up some current PCPs on production pass car engines along with the associated boost pressure as this obviously alters the PCP considerably. I will not be running an over-boost system so I'm primarily interested in steady state WOT PCPs to see how close my estimated 1724 PSI PCP relates to other real world measured data at similar boost pressures. I am aware that there are many variables in PCPs not the least of which is fuel type, octane, IAT, static compression ratio, total ignition timing, etc.

I appreciate any input. I'm sure those working in advanced engine development have moved on considerably from the currently available turbo S-I engines, which in themselves have come a long ways from yesteryear turbo S-I engines in performance, drivability, fuel economy and reliability. My goal is 100% reliability in this 3.2L VR6 turbo conversion engine. I'm not looking for extreme performance in this application.

 

[140Airpower]

"Any number of auto companies can confirm in their testing that the DI gas vaporization process in the cyl. produced such a significant drop in induced charge chamber temp that they were able to increase the static compression ratio by as much as a full point, i.e. going from 11:1 to 12:1 in numerous engines with no other changes than going from PFI to GDI. There are likely SAE papers on this if you're interested."

Just thought you might be able to cite a paper. I am interested in this because thermodynamically, the total charge cooling from the vaporization of liquid fuel should be the same between the two cases. I do expect that the cooling of hot spots can be dramatically different and that this can be a big advantage wrt octane requirement and permissible CR. Thanks.

 

[TrackRat]

The total vaporization energy exchange should be the same but when the vaporization occurs exclusively inside the cylinder it apparently is more efficient at cooling the intake charge vs. some of the cooling effect being transferred into the intake manifold or cyl. head with PFI. No one expected such a significant change but it proved quite useful for increased efficiency and eliminating of detonation.

PFI typically injects some or all of the fuel into the port with a closed valve for better vaporization, depending on the EFI strategy being employed. I know that VW is one company who raised the static compression on their 3.2L VR6 engines from ~11:1 up to ~12:1 when they changed from PFI to GDI. They were quite public about the cooling effect and compression bump so that's why I suspect an SAE paper may exist from them or other car makers who bumped the compression ratio based on the in cylinder cooling effect.

 

[durablack2]

Not only does DI offer better vaporization but you will have better fuel mixture and homogenization. In high CR and turbocharged engines, pre-ignition is one of the main limiting factors. With DI you can inject fuel during the compression stroke which will contribute to even further knock reduction because the fuel will be sprayed where you want it, and cool the cylinder during the compression stroke which is where pre-ignition occurs.

 

[TrackRat]

We're going sideways on the original topic folks... You really should start a new thread to discuss GDI.

Yes GDI is achieved at much higher injection pressures than conventional PFI and the "entire process" for the most part lends itself to cooling the intake charge and piston crown to deter detonation and allow more static compression and or more ignition timing on NA as well as boosted applications. It turned out to be an important discovery for gas engine advancement including reduced exhaust emissions and lower fuel consumption. One negative associated with GDI is that many engines tend to build up carbon deposits on the intake valves. PFI washed much of the oil vapor/carbon build-up off the intake valves that GDI engines are unable to do unless you use both PFI and GDI on the same engine as at least one auto maker has done to address the carbon build-up issue with GDI.

 

[gruntguru]

Some of the potential for CR increase is attributable to de-throttling and lean burn when operating in stratified-charge mode.

je suis charlie

 

[TrackRat]

There is no de-throttling or lean burn mode per se used in the VW VR6 model engines. As noted the vaporization/injection process lends itself to superior cooling of the air charge instead of the cooling being used to cool the valves or ports. VW uses the same T/body and induction system on the VR6 engines with PFI and GDI. When rapid combustion is cost effective for pass car use, it will provide for more refinement of the combustion process with leaner AFRs and more ignition timing if desired.

Anyone else have firsthand knowledge of PCPs on current S-I pass car engines running boost in the 2.5 bar range?

 

[durablack2]

Well stratified injection is used for fuel efficiency purposes only for production engines. Therefore the engines only operate around stoich / slightly lean (~1.2 lambda) when they can such as in low to medium load conditions. That being said the PCP's during full load are similiar to those of non-stratified burn engines during full load and are limited by things mentioned above (fuel octane, knock, preignition, etc). These stratified burn engines still require high levels of enrichment for cat protection, knock, & PI prevention much like non-stratified engines at high loads.

 

[durablack2]

*Stratified ignition (in the first sentence)

 

[140Airpower]

TrackRat, Why this "...There is no de-throttling or lean burn mode per se used in the VW VR6 model engines..."?
These expedients work for just about everybody else. It seems VW is leaving something (a lot!) on the table.

 

[140Airpower]

gruntguru, Lean burn can lead to very high exhaust valve temps and a propensity to detonation. I think that fuel spray bounced onto the exhaust valves may be the biggest influence in allowing increased CR.

 

[TrackRat]

Please use the thread below for discussions on GDI and the cooling effect on the induced air charge, etc. so this thread can remain on the subject PCPs.

http://www.eng-tips.com/viewthread.cfm?qid=412274

 

[140Airpower]

TrackRat, YOU introduced the "...discussions on GDI and the cooling effect on the induced air charge..." in this thread.

 

[TrackRat]

140airpower-

My comment on GDI charge cooling was in response to durablack2's post on PCPs in GTDI engines even though the original thread requested info. specifically on PCPs in PFI S-I engines. My comment was not intended to start a discussion on GDI combustion process and/or charge cooling, it was to note that GDI engines may have higher PCPs based on increased static compression and the ability to run higher boost than a PFI boosted engine due to the charge cooling documented in GDI engines.

 

[durablack2]

@Trackrat --- "Anyone else have firsthand knowledge of PCPs on current S-I pass car engines running boost in the 2.5 bar range? "

I read that and thought that you were asking about Stratified Ignition engines, my mistake - my job typically refers to S-I as stratified ignition (lean burn) since I work with just gasoline, no one feels the need to call out SI as a spark ignited engine... So I just realized that my comment about lean burn does not answer the question you're asking.. Although the PCP's for those stratified ignition that I mentioned are accurate...

 

[gruntguru]

"gruntguru, Lean burn can lead to very high exhaust valve temps and a propensity to detonation. I think that fuel spray bounced onto the exhaust valves may be the biggest influence in allowing increased CR."

Correctly managed, lean-burn results in reduced combustion/exhaust/valve temperatures.

je suis charlie

 

[TrackRat]

durablack2-

There was no issue for me with your comment. I understood that you were referring to GTDI engines and that is why I noted they could have higher PCPs than conventional PFI S-I engines due to the additional charge cooling.

 

[Lou Scannon]

Correctly managed, lean-burn results in reduced combustion/exhaust/valve temperatures.

Quite so. This has been known and exploited for maximum cruising fuel economy in highly developed reciprocating aero engines since the 1930s or earlier.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[TrackRat]

PLEASE keep this thread for discussions only on Turbo PFI pass car PCPs only. The thread below is for those who desire to discuss GDI charge cooling, exhaust emissions, etc..

http://www.eng-tips.com/viewthread.cfm?qid=412274

 

[HarleyE30]

Around 130 bar peak (PFI).
More reliably, 115 bar peak

 

[TrackRat]

HarleyE30- Thanks for the info. That is what I'd expect but it's always nice to have input from people with firsthand knowledge on the subject.