I was working on a genset yesterday at a location about 5100' ASL. It is 38 kw general spec but the chart shows it only does about 30.5 at that altitude. Turbocharged, propane. (The propane gets mixed in a carb and the turbo boosts it thru an aftercooler and then to the throttle) However, I set up a test and it pretty easily does the full 38 anyway at altitude. So I wonder to some of you gurus: What gives? I know some diesels have a max altitude also. I am wondering if it might be due to turbo max RPM being exceeded but I just don't know. I have another one to install at 7000 feet someday, when it finally happens.
Electronically-controlled engine I assume.? Might be interesting to get hold of the performance derate chart versus atmospheric pressure. My experience of diesels at altitudes up to 17k feet is that turbo overspeeds are much more likely. I’ve seen cases where cast aluminium compressor wheels were replaced with titanium because they couldn’t stop them exploding. Air filter restriction is critical to turbos operating at altitude. Probably not such a critical factor in a genset compared to a machine though.
Well, it is electronically controlled but just barely. Propane mixer (carb) gets slightly manipulated to satisfy an oxygen sensor, electronic throttle maintains 1800 RPM, has computer controlled timing, wastegate on turbo is a passive device not connected to ECM. I read on an airplane site about watching the wastegate position close gradually the higher altitude got, until it was closed fully and that was all the TC could do, but I don't understand the concept. Maybe that is a different set of calcs for an airplane, I don't know.
Well look at it this way maybe--before and even after-but mainly with jacketed coolant cooled aftercoolers on a truck application. Boost is always 2 to 3 psi higher at 30*, That cooler air is really obvious in a jacketed cooler over a CAC. Dense. And climbing a mountain pass that's 4,000' elevation isn't that drastic it still will produce a little more boost. In your case I don't think the engine is being worked that hard. just my 2 cents.
Yes, I am just going off their spec sheet, it states the unit (38 kw) loses x amount of performance per 1000 feet above sea level. Which is usually accurate on naturally aspirated models. But on these TC models the experience does not bear that out at all. I also verified the same on an 80 kw unit we installed on the same site last year. It has a TC GM clone 6.2 liter engine. Really little trouble to go 80 kw. In fact it goes 125 kw with more exotic TC and aftercooler. Just trying to figure out what they are getting at here. The tech support I am likely to get will probably not know anything.
Trouble is with most---engine used in application, the rating is set at or near it's peak performance level. It can produce at that level but in reality it barely sustains it.
You said it right there - thinking back I had one of these same models a couple weeks back, runs automatically and gives a phantom shutdown when nobody is around. Found the turbo blowing oil into the aftercooler, thought that was the problem, changed turbo, then when I put the load to it with new turbo, near max load it goes into compressor surge/stall/backfire thru the intake which of course leads to loss of RPM and immediate shutdown so the oil problem was something I just accidentally uncovered. Took a while of head scratching to diagnose that one, found that closing up the spark plug gaps fixed it temporarily. What I figure is there was a misfire at max load due to weak ignition, caused lack of drive to turbine, and the whole house of cards falls down.
Unrelated sort of--in early 90's I worked for a irrigation/domestic well company welding/building pump intake/discharge plenums. A diesel powered/volume/medium pressure 60 psi was ordered for a irrigation project. When it showed I looked at the peak torque/hp at rpm and the same info with supplied with pump---in this case it wasn't rocket science to figure out the 30 hp diesel was going to run it's ass off requiring all it could develop to operate pump at full rated discharge. * In 100* ambient it was constantly shutting down by murphy switch, at full tilt it was using every bit of hp/torque it could muster and constantly overheating.
17K, wow, I'll bet it is hard to keep things cool unless ambient is real low. We get up to about 9,000 occasionally and I can tell you that a naturally aspirated diesel doesn't run well, and turbo charged can heat pretty easily over 80f ambient.
Yes and no because the engine power can be so far derated that the heat output to the cooling system as a result of combustion isn’t that high. Ambient temperatures don’t get that high either, and when the sun says goodbye each evening the effect on the temperature is like someone took a hammer to the bulb on the bottom of the thermometer…….. As I said earlier, the electronic controls all work on the signal from the atmospheric pressure sensor, so although the derate can be regarded as somewhat linear with increasing altitude it’s nowhere near a straight line. Even on the same job site the derate can vary from day to day as the atmospheric pressure changes. A significant number of machine models have “high-altitude arrangement engines” that are designed to somewhat compensate for the lack of oxygen up there. No way can humans walk and talk at the same time when the atmospheric pressure is below 60 kPa.
Very interesting.