Originally Posted by RayCJ
Originally Posted by 4x4le
#2 is where I am getting confused. This is precisely how I tuned engines but I used eddy currents instead of a generator and load boxes. If the load increased at a rate that bogged the engine before the throttle was opened up then something in that test isnt right. Perhaps the engine isnt rated for those load levels at those rpms?
4x4le... Sorry for the slow reply. During the day, I do not have Internet access...
In many cases, the purpose of the tests I outlined was to establish the rating for the engine -not to test it against known values... The values were often not known. These devices were $pecial-purpo$e, to be used in places like the railroads, public utilities, mining industry etc. As such, the results had to be verified by at least 2 independent (and accredited) labs. In some cases, the reports were ultimately submitted to government agencies like the Dept of Transportation, Dept of Energy etc. That said, the goal was not to find-out if the engine was a perfect representation of the Otto cycle... the purpose was to test it under real conditions, not a 5 second zip through the RPM range.
Also, the steps I outlined were slightly simplified for the purpose of this discussion. In reality, a protocol, written and reviewed by the senior engineers (I was fresh out of college), was followed. This involved specified amounts of warm-up time, specified amounts of time under load at each RPM step etc... Significant effort went into fuel measurement. If any test could not be done according to protocol and schedule, all data was scrapped and re-done from scratch.
As for the WOT situation... There were many kinds of engines, most 4 stroke diesel, some 2 stroke diesel. Some turbocharged, some supercharged, some NA, some intercooled -and some engines were turboshafts (i.e. jet engine). All bets are off making assumptions about WOT and what the engine is supposed to be doing.
Originally Posted by Shannow
RayCJ...yes, when we were doing dyno testing at university, it was steady state, plot a curve.
The fact that modern chassis and engine dynos sweep through the RPM range either means that the true power isn't measured (some is used to accelerate for that couple of seconds), or there's fudges in there.
It's been a long time since I did this kind of work but, I'm pretty suspicious of these dyno-sweeps. I've also done a little investigation about the "inertia" dynos and they have me scratching my head.. You say there is a little fudging going on... I tend to think there's a whole chocolate factory's worth of fudge going on. I'm not seeing the light or feeling the love. Would love to tell you about a childhood story about "scratching heads" -but I think it might be over the top given the "complexity" of this thread.
Ray
Check out my first post, either page 1 or 2 I think, about where I used to do tuning for peoples scca and nasa race cars and driftcars as well as streetcars. I always used dynodynamics or dynatech which are not inertia dynos and I went into my distane for them.
Anyways I understand that there are a lot of engines that are not air throttle controlled but I can actually think of a few instances where even on a gas 4 cycle that i could bog before "max effort". It was turbo charged engines and i could actually push the turbo past its surge line at lower rpms and have on throttle surge so i had to back off the boost (still full throttle) in order to reduce the requested effort. Boost could be raised higher at higher rpms still.
I can for sure see where turbine engines could fall into this, i can see where 4 cycle turbo diesels could. I can see where naturally asperated diesels end up just making heat instead of power or hit a tip over point, and I can see where supercharged 2 stroke diesels would hit a similar wall as a 4 stroke naturally asperated diesel.
Dyno sweeps were never my thing. I always tuned steady state. I was never even looking at hp or tq when tuning but rather the effort the dyno was resisting my efforts with. After all the load cells at all the given rpms were tuned we would do a few "sweeps" at different loads to see what power it made. Tuning steady state usually had the car in perfect driving order and just made the pedal feel strong everywhere.
I think where some of the confusion came from is everyone has 4 cycle gas or diesel engines in mind with this conversation. Thinking about stationary engines that holds a given rpm does not translate well to the dynamics of a automobile engine.
Originally Posted by 4x4le
#2 is where I am getting confused. This is precisely how I tuned engines but I used eddy currents instead of a generator and load boxes. If the load increased at a rate that bogged the engine before the throttle was opened up then something in that test isnt right. Perhaps the engine isnt rated for those load levels at those rpms?
4x4le... Sorry for the slow reply. During the day, I do not have Internet access...
In many cases, the purpose of the tests I outlined was to establish the rating for the engine -not to test it against known values... The values were often not known. These devices were $pecial-purpo$e, to be used in places like the railroads, public utilities, mining industry etc. As such, the results had to be verified by at least 2 independent (and accredited) labs. In some cases, the reports were ultimately submitted to government agencies like the Dept of Transportation, Dept of Energy etc. That said, the goal was not to find-out if the engine was a perfect representation of the Otto cycle... the purpose was to test it under real conditions, not a 5 second zip through the RPM range.
Also, the steps I outlined were slightly simplified for the purpose of this discussion. In reality, a protocol, written and reviewed by the senior engineers (I was fresh out of college), was followed. This involved specified amounts of warm-up time, specified amounts of time under load at each RPM step etc... Significant effort went into fuel measurement. If any test could not be done according to protocol and schedule, all data was scrapped and re-done from scratch.
As for the WOT situation... There were many kinds of engines, most 4 stroke diesel, some 2 stroke diesel. Some turbocharged, some supercharged, some NA, some intercooled -and some engines were turboshafts (i.e. jet engine). All bets are off making assumptions about WOT and what the engine is supposed to be doing.
Originally Posted by Shannow
RayCJ...yes, when we were doing dyno testing at university, it was steady state, plot a curve.
The fact that modern chassis and engine dynos sweep through the RPM range either means that the true power isn't measured (some is used to accelerate for that couple of seconds), or there's fudges in there.
It's been a long time since I did this kind of work but, I'm pretty suspicious of these dyno-sweeps. I've also done a little investigation about the "inertia" dynos and they have me scratching my head.. You say there is a little fudging going on... I tend to think there's a whole chocolate factory's worth of fudge going on. I'm not seeing the light or feeling the love. Would love to tell you about a childhood story about "scratching heads" -but I think it might be over the top given the "complexity" of this thread.
Ray
Check out my first post, either page 1 or 2 I think, about where I used to do tuning for peoples scca and nasa race cars and driftcars as well as streetcars. I always used dynodynamics or dynatech which are not inertia dynos and I went into my distane for them.
Anyways I understand that there are a lot of engines that are not air throttle controlled but I can actually think of a few instances where even on a gas 4 cycle that i could bog before "max effort". It was turbo charged engines and i could actually push the turbo past its surge line at lower rpms and have on throttle surge so i had to back off the boost (still full throttle) in order to reduce the requested effort. Boost could be raised higher at higher rpms still.
I can for sure see where turbine engines could fall into this, i can see where 4 cycle turbo diesels could. I can see where naturally asperated diesels end up just making heat instead of power or hit a tip over point, and I can see where supercharged 2 stroke diesels would hit a similar wall as a 4 stroke naturally asperated diesel.
Dyno sweeps were never my thing. I always tuned steady state. I was never even looking at hp or tq when tuning but rather the effort the dyno was resisting my efforts with. After all the load cells at all the given rpms were tuned we would do a few "sweeps" at different loads to see what power it made. Tuning steady state usually had the car in perfect driving order and just made the pedal feel strong everywhere.
I think where some of the confusion came from is everyone has 4 cycle gas or diesel engines in mind with this conversation. Thinking about stationary engines that holds a given rpm does not translate well to the dynamics of a automobile engine.