WhiteBlue wrote:Edis, your considerations are certainly useful for an air limited formula but the discussion here was meant for fuel flow limited F1 turbo engines. At least a big part of it. If you check the 2014 rules they do not allow a significant portion of the fuel to be port injected. If memory serves me right it is just 20%. So if you are committed to inject the vast majority of the fuel shortly before TDC you are going to use the most efficient combustion method available to you. And that is spray guided AFAIK. Spray guided combustion achieves a certain amount of stratification by design and the rules leave some head room for even faster injection than we know from todays existing 200 bar systems. They are allowed to use 500 bar. The engines will not go much beyond 10,500 rpm either because they will be fuel starved above that limit.
I cannot answer the question what kind of AFR they will be using at different power levels but I'm confident that they plan to burn leaner than the current crop of air limited engines. The logic of the formula enforces that strategy. As I have said before I'm not working in the field but I can read the rules and I believe that your proposal does not fit the new rules from 2014. So I would be interested to learn what you think will be the injection method for a 2014 project according to your best information.
I haven't said anything about port injection. It's normal practice for direct injected spark ignition engines to inject fuel during the intake stroke at high loads; they do this by injecting the fuel directly into the cylinders without having port injectors.
WhiteBlue wrote:If I read you right you deny that the turbocharged engine will be intrinsically more fuel efficient than a NA engine. I find that hard to believe. If you go back to the example of the Porsche Cayenne V8 engine you will find a discrepancy with your statement. Porsche did not downsize the engine but added a turbocharger in order to raise the power. If you look at the figures they suggest that the turbocharged version is considerably more fuel efficient than the naturally aspired version. This is also what the Garrett expert whose words opened this thread suggest for a road going engine. He said that you turbocharge for better driving experience and fuel efficiency.
When you turbocharge a spark ignition engine it's efficiency will drop slightly, yes. That shouldn't come as a surprise to anyone with basic engine knowledge, spark ignition engines are after all knock limited. In other words, the first thing you do with an engine when you turbocharge it is lower it's compression ratio and/or reduce spark advance and/or enrich the fuel mixture to avoid knock, all of which will reduce engine efficiency. If it's a passengar car engine you generally don't want to reduce compression ratio more than you need given that this will impact part load efficiency.
As for the turbo expert, he never claimed engine efficiency increase when you turbocharge an engine, what he said was:
"Comparing horsepower-to-horsepower, a turbocharged engine consumes less fuel in day-to-day use, than a non-turbocharged car does."
This is true due to downsizing.
Diesels don't suffer from this problem due to the fact that they are not knock limited.
WhiteBlue wrote:If we look at the last time we had turbos going against NA engines in F1 it certainly looked like the turbos were more fuel efficient than the NAs.
This comparison will say nothing. The V6 turbos had significantly more power, yet a much smaller fuel allocation, so improving fuel consumption was important, otherwise you had a lot of engine power that you couldn't use. The naturally aspiranted engines has a larger fuel allocation, but also a significant power handicap compared to the turbocharged engines. So for these engines saving fuel was of no concern, the lack of power was however. So output had to be maximized, regardless of efficiency.
It can also be interesting to note that horesepower- for-horsepower, the turbocharged engines had slightly slower lap times. At least that was what Brabham concluded, having compared the turbocharged BMW and the NA Cosworth.
WhiteBlue wrote:There is also the indisputable fact that adding a turbocharger will reduce the kinetic and thermal energy level of the exhaust gas at the tail pipe. All other things being equal that necessitates a higher efficiency of the turbocharged engine. The turbo engine can convert that energy difference into useful power that is wasted by the NA engine.
The energy extracted by the turbine does not contribute to the useful output of the engine. Instead the turbine power is used by the compressor to increase charge density. So, the thermal energy extracted from the exhaust is simply cooled off in the charge cooler, or contribute to a higher pre turbine exhaust temperature.
WhiteBlue wrote:I'm not saying that downsizing profits only from turbo charging. There is also the aspect of the improved mechanical efficiency that you describe. Both effects are contributing to the success of downsized engines. It would be wrong IMO to deny any of the two effects their contribution to the efficiency improvement.
Downsizing profits of downsizing, not turbocharging. Please read "Turbocharging the internal combustion engine" by Waton and Janota if you want more info on the subject. Even after thirty years, this book still offers the most in depht coverage of turbocharging, and is commonly used as a reference by people in the field.
WhiteBlue wrote:For another comparison I have researched what BMW did with their 1series 2L diesel engine. They basically sell the same engine in NA, low boost turbo and high boost turbo version.
116d -- 85 kW -- 4.5 L/100km -- 0.0053 L/100km*kW
118d --105 kW -- 4.5 L/100km -- 0.0042 L/100km*kW
120d --130 kW -- 4.7 L/100km -- 0.0036 L/100km*kW
If we set the 120d high boost turbo as 100% base line we find:
120d 100% baseline fuel consumption per power
118d 119% of baseline fuel consumption per power
116d 146% of baseline fuel consumption per power
I think the figures speak for themselves. The same basic engine becomes more powerful the higher the boosting is done. At the same time the mild boost comes without any increase in fuel consumption and the high boost produces massive additional power with very little additional fuel consumption. The logic tells us that the improved power specific fuel consumption is directly related to the size of the turbine that reclaims the boosting energy from the exhaust gas. Although this example is from a diesel engine the energy balance will work similarly in a petrol engine. In a petrol engine it is slightly more difficult because high injection pressures and controlling the ignition and combustion is more of a problem.
Your logic is flawed, the only thing you can tell from those numbers is that the higher output engine is less fuel efficient that the two less powerful engines and that a more powerful engine won't consume that much more fuel than a less powerful one, given that you actually don't use the higher output the engine can produce. Keep in mind here that all engines are doing the same work in the New European Driving Cycle (NEDC).
For arguments sake, lets compare two electric motors using your logic. Both motors produce the 10 kW we need to perform our test, but one offers a maximum output of 50 kW and the other 100 kW. The 50 kW motor consume 11 kW electricity while producing 10 kW and the more powerful motor 12 kW producing the same 10 kW output. Now, should we praise the "improved power specific fuel consumption" of the more powerful motor, or should we realise the fact that the more powerful engine is simply less efficient? Our test will of course tell us nothing how efficient these engines are at a higher load, and that is also the case with the NEDC. In the NEDC a lot of time is spent idling, the maximum rate of acceleration is the equivalent of 0-100 km/h in something like 30 seconds and the highest speed during the test is 120 km/h. Since all engines are tested in the same car, the amount of energy produced by the engines during the test should be the same.
All the BMW diesels are also turbocharged, and since they are diesels they are not affected the same way as gasoline engines. With gasoline, the lower output versions could use a higher compression ratio given the lower boost pressure.
