Printable View
Some numbers on the Garrett GT22 turbine.
It can produce ~39kw of shaft power from 700C exhaust at 3,400rpm on our engines. That's enough for ~28psi boost. Drive pressure would be ~38psi allowing 5psi exhaust backpressure.
T25 turbine would produce about 4psi more backpressure to do the same job.
I'm pinning my plans on the TD04HL turbine which I don't have maps for, but is the same trim and slightly larger than the GT22 turbine.
Corrected mass flow is:Quote:
Originally Posted by Dougal
Mass flow corrected = Mass flow x (Pref / Pin) x square root (Tin / Tref)
Phi = Mass flow x square root (T) / P
where temperature T and pressure P in both cases are absolute values.
So in essentially both approaches are correcting the mass flow. What we don't know for Garrett turbine maps is what reference temperature and pressure they base their turbine maps on.
Actually those curves in the turbine maps, are disguising the full picture, they are a simple fit through a larger set of data curves. See the pic below.
With the T25, or GT22 turbines, for our purposes, it appears that their waste gates are not flowing enough at the higher engine rpm's. It is a long time since I have looked at these and have to wonder if it would be practical, or possible to port them to improve the flow.
Also adding preload from the actuator to increase boost would, I suspect be counterproductive for satisfactory flow through the waste gate. A good boost controller can be better for this purpose.
I note that the EFR turbos have quite large waste gates, and the ports have been designed for good flow, this with a larger turbine.
The GT22??V with it's largish turbine housing could be a good solution, given a good control system for the vanes that doesn't cause to much restriction during cruise. Though as we know, the turbine maps don't seem to be available.
When the exhaust flow is above the curve for the turbine, the excess needs to be set out through the waste gate, as the curve depicts what the turbine can handle.
If the exhaust flow lies below the curve, the turbine is too large and it's performance will not be as good as one where the curve matches the flow.
I used their compressor reference temperature and 1 bar for reference pressure. This made the result as expected, but it could certainly be out by a few degrees or pascal's.
I am getting very little wastegate flow in my calculations. The gt22 turbine flows roughly 30lb/min in real terms at 700c.
The t25 turbine at 750c chokes out at roughly 24 lb/min. Interestingly this was a near perfect fit for where my engine would choke the exhaust and hit the wall power wise at 2500rpm and full load with the wastegate clamped.
I'm not convinced the wastegate needs to be bigger. I cannot develop any measurable boost at 700c egt with the wastegate actuator disconnected.
Lower temperatures allow higher real mass flows through the turbine. But less power is extracted too.
My understanding is that turbo manufactures, develop their turbine (and maps) using "hot gas stands".
For that reason I would expect that the reference temp and pressure, would be the inlet conditions of the hot gas stand. However they could correct them to "standard conditions", but why expect them to do that for a turbine when they don't correct compressor maps to "standard conditions".
If the high drive pressure is not down to the waste gate, then I would suspect that the turbine size may be a little small and so require such a high expansion ratio to develop the required torque/power.
To save me going back through all of your data and posts, for comparison, what drive to boost ratio results did matchbot give for the EFR turbos?
The efr turbos were generally getting drive pressure below boost for most of the full load range. Some high rpm points were drive above boost by several psi.Quote:
Originally Posted by Bush65
The efr turbines are larger, but also more efficient which almost completely offsets the size difference. I do have in my calcs the phi number bw use to compare against the garrett turbines.
It appears the new generation garrett turbines applicable to us are the gt22 and largest of the gt28.
The gt25 and smaller gt28 are old style with poor efficiency.
I can`t even begin to understand half of what you fellas are discussing :confused:
I brought this up before but it must have got missed .Is there any advantage in being able to advance the injection timing other than at start up? Your opinions greatly appreciated but please remember you are talking to an idjit;)
Thanks AM
I'm not sure where this question is leading, thus not sure how to answer.Quote:
Originally Posted by Ancient Mariner
You are no doubt aware that there is an automatic timing advance unit on the FI pump, for when the engine rpm changes.
My injection pump has a ECU controlled advanced timing interval on startup for smoke control as I wont be running a ECU I could control it with a manual switch and was curiousQuote:
Originally Posted by Bush65
as to being any advantage at other revs .Sorry about the vague query
Thanks Noel
OK.Quote:
Originally Posted by Ancient Mariner
Do you know, if by manually controlling the normally ECU controlled start-up timing advance, if it would affect the injection timing across the range of the auto advance curve, such that it would simulate a change to the static advance?
If so, then if you made it so the injection timing could be easily adjusted from inside the cab, it could be useful for finding the best static advance setting for the injection. You may find, there are optimum settings for torque/power and economy for different vehicle loads, different ambient conditions, such as temperature and air density changes with altitude.
Regarding your first comment in the earlier post:
I'm willing to clarify/expand any technical issues. Your not the first to express those sentiments in this thread.Quote:
Originally Posted by Ancient Mariner
So I will make a start later today. I think it may be useful to start from the beginning and spread it over a number of post for each topic. It will take some time and I won't have any this Friday or Monday.
Given the title of this thread, I trust Dougal won't see this as a hijack. If so I can take it to a new thread.
While there are other ways to begin the selection procedure for a turbocharger upgrade on a diesel engine, the method discussed in this post starts with determining the air mass flow rate necessary to meet the desired power output. Air mass flow rate is the mass of air passing through the engine (and turbocharger) in a given time. It has units of kg/s (or lb/min).
Before we can determine the air mass flow, we need to know how much fuel has to be burnt in the combustion chamber to achieve the desired power output. For this we use the SFC (Specific Fuel Consumption), which is the amount of fuel required to produce one unit of power at full load. It has units of gram/kW.hour (or lb/HP.hour).
The lower the SFC, the less fuel required to produce the power. Or how effectively the engine converts the potential chemical energy of the fuel into mechanical energy. Combustion efficiency is a large factor, and the modern turbocharged and intercooled, direct injection diesel engines achieve the lowest SFC. Another important factor is mechanical loss, e.g. friction between moving parts.
With regard to diesel combustion some details that reduce SFC are:
- Turbocharging
- Intercooling
- Finer fuel atomisation. Unlike petrol, diesel fuel is not vaporised, but atomised as small droplets by the fuel injectors. The smaller the droplets, the larger the total surface area of the total fuel injected each cycle, which allows better combustion. Better atomisation is achieved by using smaller nozzle holes, but demands more holes, and/or higher injection pressure to produce the the required fuel mass flow rate in the short duration available.
- Better mixing of fuel and air. With small diameter cylinder bores and direct injection, swirl needs to be produced by the inlet ports. Modern engines with four valve heads allow the fuel injector to be located on the centreline, which produces better mixing.
So what SFC to use for the Isuzu 4BD1? Here we are fortunate because Isuzu has published diagrams with the SFC over the rpm range. The pic below shows the diagram for the post 1988 4BD1T.
BTW, the best rpm for fuel economy is approximately where SFC is least.
http://www.aulro.com/afvb/attachment...erformance.jpg
If we multiply the desired peak power at 3000 rpm by the SFC at the same rpm, we have the required mass fuel rate per hour. Divide this by 3600 to give mass fuel rate per second.
Given the mass fuel rate we can now calculate the required air mass flow rate.
The criteria now is the required ratio of air mass flow to achieve complete combustion of the fuel. If there is insufficient air, black smoke will be emitted from the exhaust and high EGT will result. If there is to much air, power will have wasted. At peak power rpm, an air/fuel ratio of 18 to 20 is a good figure for a starting point.
To calculate the required air mass flow rate, multiply the fuel mass flow rate by the air/fuel ratio.
In the next stage we determine the pressure ratio required to realise the air mass flow and we will be on the way to selecting a suitable turbocharger compressor.