![]() |
If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
![]()
Hi Gord,
Not so much on us automotive engineers today... A lot of modern automotive engines are run right along the knock limit for efficiency, with knock control constantly operating. To do this, there has to be a knock event every now and then for the knock control to be able to detect the limit. (Knock control just detects knock events and retards the ignition. When there is no knock, ignition is advanced again until the next knock occurs.) This normally works fine. However on some (not all) engine types, on high load testbed runs this has recently led to very rare statistical occurence of "super-knock" events, with disastrous results. Yes, that's quite interesting to me, and it backs my opinion of using low test fuel in my cars...I never use high test fuel at all, mind you, I only use standard domestic vehicles but I consider high test wasteful in modern engines with 'knock control'. Well, it depends... Normally you won't damage an engine with knock control by using lower grade fuel than recommended, however within limits. If you use very low octane fuel on a high compression or a turbocharged engine, ignition might occur before the spark just from the compression, as we discussed. There is nothing knock control can do about that. Also, depending on your driving profile, you might find that fuel consumption increases with the lower grade fuel, as retarded ignition reduces engine efficiency. This is especially valid at high engine loads and low engine speed, where the biggest retard is neccessary. Wether the increase in consumption will eat up the price advantage of the lower grade can only be determined by experiment. Yes, I understand that, another good system that GAMI is looking at is their accurate fuel injectors to enable automobile engines to be run lean. Now that is a new one to me! I know about GAMIs injectors for GA piston engines and all the LOP-operation stuff, wich are around for a while now, and which I think are a big improvement. I didn't know that they are planning on entering the automotive market and I'm quite surprised. Automotive engines, different from aviation, run stoechiometric basically anywhere on the map exept full load. (stoechiometric mixture is more or less peak EGT). Due to their design, mostly liquid cooled, temperatures are not a problem. Of course you could run such an engine lean (LOP), but you won't pass any emissions test for sure. I don't think you really need special injectors to do it, but you would need to retune the ECU. And the fuel savings compared to running stoechiometric are only a fraction of what you save if otherwise you have to run rich. The Japanese car makers had lean running engines on the market for a while, and some of the direct injection gaoline engines being developed now also run lean by creating a stratified charge. But that's far beyond an aftermarket improvement. We run (perhaps ran might be more accurate) large recip aircraft engines at '10% lean from best power' (by manually leaning them during cruise) for many thousands of hours and they worked fine in that condition, matter of fact they'll continue to run fine as much as about 30% lean before they get unstable, they seem to love lean mixtures!... Do you by chance know whether these had direct injection (injecting the fuel into the cylinder instead of the manifold)? To my knowledge there have been direct injection piston engines among the big radials, but I haven't found any further information about it so far. regards, Friedrich -- for personal email please remove "entfernen" from my adress |
#2
|
|||
|
|||
![]()
"Friedrich Ostertag" wrote:
We run (perhaps ran might be more accurate) large recip aircraft engines at '10% lean from best power' (by manually leaning them during cruise) for many thousands of hours and they worked fine in that condition, matter of fact they'll continue to run fine as much as about 30% lean before they get unstable, they seem to love lean mixtures!... Do you by chance know whether these had direct injection (injecting the fuel into the cylinder instead of the manifold)? To my knowledge there have been direct injection piston engines among the big radials, but I haven't found any further information about it so far. regards, Friedrich Well, just a comment about domestic automobiles, I didn't mean to indicate that I operate them below the manufacturers specified octane ratings, after all, I believe that the manufacturer knows his engine best and I'd never try to second guess him, but I have all kinds of friends and relatives who use hi octane fuel in their cars even though low octane is recommended. (complete waste I feel) Another thing that I NEVER do is 'recommend to anyone' what fuel to use. You're bound to get blamed sometime in your life because a friend's wife got preggy if you do... ![]() About the direct injection, the Argus (ASW aircraft) used by the Canadian Armed Forces had Wright R-3350-EA1 engines (3700 BHP) which had direct fuel injection into the cylinder (not just prior to the intake valve). The Wright R-3350-89A fitted to the Fairchild C-119 Packet had 'spinner injection', where the fuel was injected into the spinner of the supercharger, and the P2V-7 Neptune was set up this way too. -- -Gord. |
#3
|
|||
|
|||
![]()
Hi Gord,
Well, just a comment about domestic automobiles, I didn't mean to indicate that I operate them below the manufacturers specified octane ratings, after all, I believe that the manufacturer knows his engine best and I'd never try to second guess him, but I have all kinds of friends and relatives who use hi octane fuel in their cars even though low octane is recommended. (complete waste I feel) Ah, you're absolutely right there! Sorry for the misunderstanding. There is no point in using higher octane than what the engine was designed for. Even knock control will not advance ignition beyond the calibrated map for the designated fuel. However a lot of people over here fell for a marketing trick of Shell Oil: Instead of the 98 octane highest grade fuel sold in Germany and most euroean countries they offered a 100 octane (by the way, this is ROZ, not ROZ+MOZ/2 as in the US) fuel called "V-power" with supposedly all kinds of mysterious additives at 10 ct / Liter premium over other oil company's 98 octane. Lots of car magazines and also the ADAC (your AA) tested it in various models and found no difference whatsoever in power and consumption. Yet Shell sells 10% of it's turnout in V-Power while the other's only sell 5% 98. Talk about snake oil... Another thing that I NEVER do is 'recommend to anyone' what fuel to use. You're bound to get blamed sometime in your life because a friend's wife got preggy if you do... ![]() :-) About the direct injection, the Argus (ASW aircraft) used by the Canadian Armed Forces had Wright R-3350-EA1 engines (3700 BHP) which had direct fuel injection into the cylinder (not just prior to the intake valve). The Wright R-3350-89A fitted to the Fairchild C-119 Packet had 'spinner injection', where the fuel was injected into the spinner of the supercharger, and the P2V-7 Neptune was set up this way too. I always find it intriguing, that almost everything we develop today as supposedly latest techology has been there half a century ago. The only really new thing in engines today is electronic control. regards, Friedrich -- for personal email please remove "entfernen" from my adress |
#4
|
|||
|
|||
![]()
"Friedrich Ostertag" wrote:
I always find it intriguing, that almost everything we develop today as supposedly latest techology has been there half a century ago. The only really new thing in engines today is electronic control. regards, Friedrich Exactly...and it's one of the reasons that, although I consider myself quite knowledgeable engine wise, when I open the hood of an ailing engine I quickly close it and get on the fone for a towtruck...there's just so much complication in all the electronic sensors, computers etc to squeeze every ounce of efficiency out of a litre of fuel that I find it daunting. My wife's Corolla just finished it's lease and I bought it and leased another Toyota for her. A 'Matrix'. They have an intriguing feature called VVTi (Variable Valve Timing). Neat system!...hope it's rugged!... Cheers -- -Gord. |
#5
|
|||
|
|||
![]()
On Sat, 24 Apr 2004 17:29:50 GMT, "Gord Beaman" )
wrote: "Friedrich Ostertag" wrote: I always find it intriguing, that almost everything we develop today as supposedly latest techology has been there half a century ago. The only really new thing in engines today is electronic control. regards, Friedrich Exactly...and it's one of the reasons that, although I consider myself quite knowledgeable engine wise, when I open the hood of an ailing engine I quickly close it and get on the fone for a towtruck...there's just so much complication in all the electronic sensors, computers etc to squeeze every ounce of efficiency out of a litre of fuel that I find it daunting. I like to think I know a pretty decent amount about engines, enough to do my own maintenance when I was too poor to go to garages. But when I got the Puma, I didn't even bother opening the bonnet. I knew I wouldn't recognize much of what was under there and that the key things would be hidden from view. All I needed to convince me that the running gear was in excellent shape was a flying trip down the local dual carriageway :-) (Happily 3 years later nothing serious has gone wrong) My wife's Corolla just finished it's lease and I bought it and leased another Toyota for her. A 'Matrix'. They have an intriguing feature called VVTi (Variable Valve Timing). Neat system!...hope it's rugged!... This is on the Puma too, as Variable Cam Timing. I think it's fairly failsafe. Taking a mechanical engineer (which I'm not - I'm an elec) view, I'd say they do it by retarding/advancing the valve timing according to revs and load. So if the system fails or degrades, the valve timing wouldn't adjust but the cams would still go round and the valves would go up or down. Not heard of rampant engine trouble in the variable timing cars so they must have got it licked. It seems to work on the Puma ... I moved from Rover 2.0 16 valve to Ford 1.7 16 valve and the Ford unit has just about equal power but it's far more flexible across the rev range. The Rover unit was fairly quiet until about 3250 rpm where it would take off. The Ford unit has usable power down at about 1800/2000 rpm. Pete Lilleyman (please get rid of ".getrid" to reply direct) (don't get rid of the dontspam though ;-) |
#6
|
|||
|
|||
![]()
"Friedrich Ostertag" wrote:
I always find it intriguing, that almost everything we develop today as supposedly latest techology has been there half a century ago. The only really new thing in engines today is electronic control. regards, Friedrich Exactly...and it's one of the reasons that, although I consider myself quite knowledgeable engine wise, when I open the hood of an ailing engine I quickly close it and get on the fone for a towtruck...there's just so much complication in all the electronic sensors, computers etc to squeeze every ounce of efficiency out of a litre of fuel that I find it daunting. My wife's Corolla just finished it's lease and I bought it and leased another Toyota for her. A 'Matrix'. They have an intriguing feature called VVTi (Variable Valve Timing). Neat system!...hope it's rugged!, looks expensive if it comes adrift in flight... ![]() Cheers -- -Gord. |
#7
|
|||
|
|||
![]()
On Fri, 23 Apr 2004 21:58:30 +0200, "Friedrich Ostertag"
wrote: Hi Gord, Well, just a comment about domestic automobiles, I didn't mean to indicate that I operate them below the manufacturers specified octane ratings, after all, I believe that the manufacturer knows his engine best and I'd never try to second guess him, but I have all kinds of friends and relatives who use hi octane fuel in their cars even though low octane is recommended. (complete waste I feel) Ah, you're absolutely right there! Sorry for the misunderstanding. There is no point in using higher octane than what the engine was designed for. Even knock control will not advance ignition beyond the calibrated map for the designated fuel. However a lot of people over here fell for a marketing trick of Shell Oil: Instead of the 98 octane highest grade fuel sold in Germany and most euroean countries they offered a 100 octane (by the way, this is ROZ, not ROZ+MOZ/2 as in the US) fuel called "V-power" with supposedly all kinds of mysterious additives at 10 ct / Liter premium over other oil company's 98 octane. Lots of car magazines and also the ADAC (your AA) tested it in various models and found no difference whatsoever in power and consumption. Yet Shell sells 10% of it's turnout in V-Power while the other's only sell 5% 98. Talk about snake oil... Definitely agree with you there ... The Puma that I have has a reaction to the higher octane 98 RON Optimax fuel that Shell sell over here. It's not a good reaction, like increased power or economy, it's a bad one. The bad reaction takes the shape of the engine management struggling for the first couple of miles to get used to the differing octane rating. Symptoms included poor running including reluctance to idle. I suspect that the anti-knock control was self adjusting itself for the increased octane rating. It also takes a little while to get used to 95 RON unleaded when that goes back in. Anyway, no measurable economy improvement (I nerdishly track my mpg) and no perceptible power improvement. Although other people reckon they see power improvements with other cars. Pete Lilleyman (please get rid of ".getrid" to reply direct) (don't get rid of the dontspam though ;-) |
Thread Tools | |
Display Modes | |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
AOPA Stall/Spin Study -- Stowell's Review (8,000 words) | Rich Stowell | Aerobatics | 28 | January 2nd 09 02:26 PM |
General Aviation Legal Defense Fund | Dr. Guenther Eichhorn | Aerobatics | 0 | May 11th 04 10:43 PM |
General Aviation Legal Defense Fund | Dr. Guenther Eichhorn | Aviation Marketplace | 0 | May 11th 04 10:43 PM |
Here's the Recompiled List of 82 Aircraft Accessible Aviation Museums! | Jay Honeck | Home Built | 18 | January 20th 04 04:02 PM |
Associate Publisher Wanted - Aviation & Business Journals | Mergatroide | Aviation Marketplace | 1 | January 13th 04 08:26 PM |