Downsized charged engines, peak cylinder pressures?
Downsized charged engines, peak cylinder pressures?
(OP)
Hi guys,
Just wondering what typical peak cylinder pressures are for these new breeds of downsized turbocharged gasoline engines we're beginning to see ?
Cheers,
Harley
Just wondering what typical peak cylinder pressures are for these new breeds of downsized turbocharged gasoline engines we're beginning to see ?
Cheers,
Harley





RE: Downsized charged engines, peak cylinder pressures?
Average pressure though... much much higher.
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
- Steve
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
- Who these days is developing a high performance non-turbocharged diesel engine?
- Are we talking about a smokey exhaust or what? I've visualizing an exhaust plume that a squid would be proud of.
Does anyone know of a case in point?"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Downsized charged engines, peak cylinder pressures?
The fuel is always going to the limiting factor to peak pressures. With turbocharging however, it is not about peak pressure.
Here's a modelled Otto cycle for comparison for two engines.
The green trace is a NASP engine of 11:1 compression, with 45° ignition advance.
The blue trace is the same engine boosted to 1 bar. Ignition timing reduced to 16° so that the peak cylinder pressure remains the same as the NASP model.
The difference is quite clear. The boosted engine maintains a significant advantage in pressure throughout the power stroke, despite have no gain in peak pressure.
In reality, a boosted engine may be able to handle a small gain in peak as well, but the majority of the gain comes from average pressure.
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
The delayed heat release equates to lower indicated efficiency, all other things being equal. Of course, assuming the turbocharged engine is downsized accordance with its higher BMEP, there should be a relative increase in mechanical effiency, and significant reduction in engine mass, which should cascade onto lower vehicle mass, even with the same vehicle interior dimensions and load capacity.
Since we're only looking at one operating point, I can only speculate what the comparison of brake efficiency looks like over a realistic drive cycle, and what the actual fuel economy comparison would look like considering the difference in vehicle mass, not to mention the probable reduction in average pumping losses for the downsized engine.
Getting back to peak cylinder pressures; it seems that the cutting edge for commercial diesel engines these days is around 3000 psi. I think it's fair to assume we're talking about iron heads and steel piston crowns here. In the case of an Otto-cycle engine, neither of these are helpful for avoiding knock, compared to aluminum, but at least they can handle higher levels of mechanical & thermal stress; which might buy some knock margin on the mechanical side, assuming the rest of the vulnerable components (fire rings, bearings, rods, spark plugs, head gasket) are equally up to the task.
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Downsized charged engines, peak cylinder pressures?
http://blackartdynamics.com/Engine/EngineThermodyn...
It's still a work in progress. I'd welcome any feedback!
RE: Downsized charged engines, peak cylinder pressures?
In my experiences, turbocharging small block Ford's in 3800 lbs cars, fuel economy usually increases from 22-26mpg N/A to 28-31 mpg under similar cruising conditions
RE: Downsized charged engines, peak cylinder pressures?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
The more efficient you make an engine at a given state, the more performance and economy you will return at that state.
This is currently one of the primary 'pushes' in the industry and why a lot more vehicles are being manufactured factory turbocharged in an effort to increase economy and as a result performance as well.
RE: Downsized charged engines, peak cylinder pressures?
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Downsized charged engines, peak cylinder pressures?
So, if you are getting the kind of gain in economy you say you are getting, your installation would be of extreme interest. Can you please describe in detail?
RE: Downsized charged engines, peak cylinder pressures?
the gains are accredited to the reduction in pumping losses
In theory you have pumping gains from the exhaust heat energy used to spool the turbine which would otherwise be pumped out of the exhaust pipe with the majority being wasted energy
RE: Downsized charged engines, peak cylinder pressures?
Auto installations are high back pressure so you can have quick turbo response. They have waste gates to limit boost on top. It's a different approach. Even with diesel auto engines I'd like to see how it's done for increasing cruise efficiency. I bet variable nozzle geometry is where you start.
RE: Downsized charged engines, peak cylinder pressures?
The same applies for cylinder filling using airflow modeling and valve timinge this is why properly designed naturally aspirated engines are capable of exceeding 110% volumetric efficiency.
While the turbocharger isn't creating positive pressure (boost) during cruising conditions it is still supplying high velocity air. This is evident by removing the compressor discharge piping while the engine is running, you can feel the airflow by placing your hand in the airstream, the turbocharger (if its properly sized) will be moving sufficient airflow to perhaps dry your hands. Some higher horsepower engines have larger turbocharg that do not even spin at idle... how's that for back pressure?
RE: Downsized charged engines, peak cylinder pressures?
This is relative. There are low back pressure systems that work primarily on exhaust gas velocity. These are called blow-down systems. The alternative is the pressure system. I have never seen an auto installation that was not a pressure system. One guarantee that a system has appreciable back pressure is the presence of a waste gate. Waste gates work by bleeding off back pressure and they work best, most precisely and over the greatest range when the back pressure in their absence would be very high. This implies that the turbo itself is a severe exhaust restriction and the combination of turbo, waste gate and associated plumbing is more restrictive than a good NA exhaust system.
"While the turbocharger isn't creating positive pressure (boost) during cruising conditions it is still supplying high velocity air".
This is what is inconsistent. A gas engine at cruise is highly throttled, producing a small fraction of its WOT power. It runs a manifold VACUUM. A turbo producing "high velocity air" is fighting the throttle while costing power in the form of back pressure.
It is very easy to gain power from adding a turbo to an existing NA engine, but gaining mpg? and especially in the amounts you claim? You have not provided details of how this was done.
I believe you would need to do mods to the NA engine, probably including exhaust gas recirculation and direct injection.
RE: Downsized charged engines, peak cylinder pressures?
Exhaust delta presure is vital to proper engine operation, and turbos are restrictions but the wastegates primary purpose is not to limit back pressure although thats the effect, the wastegates purpose is to bypass exhaust gas from overspooling the turbo to limit compressor airflow, often the wastegate vents to atmosphere
The wastegate only opens when the reference line (typically manifold pressure) exceeds the diaphragm spring pressure (desired boost pressure) this usually occurs at approximately 4000 rpm at WOT for the majority of the engines I play with. Some engines where boost is increased to the compressor maps surge limit, the wastegate never opens. Typically a properly sized turbo should flow at least 300 cfm more than what the engine will be ingesting.
As for throttle angle, a typical 4300 lb vehicle (loaded with typical payload) maintaining a 70mph cruise with a slight headwind of 1-3 MPH and a vehicle drag coefficient of 0.31, final drive ratio of 2.07:1 with approx. 22% drivetrain loss at an engine speed of 2000 rpm, the engine ingests a steady 52 cfm at 20% throttle, this was at 18 ft above sealevel engine coolant temperature of 210 degrees F and aircharge temps of 122* F barometric pressure approx 30.08, humidity of 87% with ambient temperature of 83* F, this was averaged over 24 miles (causeway bridge) on 3 different days of similar weather.
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
No other changes were made
That same engine with a supercharger averaged 22mpg
RE: Downsized charged engines, peak cylinder pressures?
Since operating the turbo creates a net loss of energy through heat dissipation and the exhaust pressure required to rotate the turbo, yet produces the same cylinder pressure as the N.A. version, how can that loss of energy be improving rather than reducing the vehicle's economy?
I concede such may be possible if the turboed engine's componentry and tune was optimised but, apart from removing the turbo, was left unchanged for the N.A. test - -
Maybe you've omitted key information, such as the N.A. engine was a larger capacity unit than the turboed engine - -
Tekton
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Downsized charged engines, peak cylinder pressures?
You have to have done some special and unusual things to get the results you claim. Otherwise, what you say is not credible.
RE: Downsized charged engines, peak cylinder pressures?
Regarding turbocharging increasing fuel economy with no mods-
when did the workshop-mechanics equipped with dremel and seat of the pants dynos invade these forums?
www.auto-scape.com
Sideways To Victory!
RE: Downsized charged engines, peak cylinder pressures?
its statistically significant because the vehicle can travel a greater distance without refueling, one of the primary factors of engineering design is efficiency which comes only second to safety
As for not being credible, I'm appalled you would even insinuate I'm being dishonest, what benefit could possibly be ascertained from spreading mistruths?
Perhaps you aren't aware that the knowledge we gain in life is only temporary, when we pass on that knowledge does us no good.
I've tuned several hundred engines I have yet to have a single 1 get less fuel economy than it did prior to being boosted, in other words I have yet to have a single engine not get better fuel economy when boosting abilities were added.
As I said prior there's nothing more that can be said, if anyone cares to elaborate as to the physics behind the increase in economy then go right ahead otherwise your spreading mistruth about something you cannot comprehend.
RE: Downsized charged engines, peak cylinder pressures?
At 20% throttle your turbo will not be doing anything much.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Downsized charged engines, peak cylinder pressures?
First, the supercharger will increase the total compression of the engine, fully equivalent to increasing the CR. It does this because it increases the air intake per cycle while the combustion chamber volume remains the same. So, it can result in the necessity to use a fuel with a greater octane number. This means that fuel costs may increase and the engine's ability to take supercharging is ultimately limited from this effect.
Assume we take a 3.8L engine and add a positive displacement supercharger (like a Roots type) that increases the breathing capacity by 20%. Now the engine has a volumetric capacity that is 20% greater than before. For all intents and purposes it behaves as a 4.56L engine. That means that at cruise it has the pumping losses of a 4.56L and a pure and unavoidable decrease in economy compared to its unsupercharged state as a 3.8L.
However, there are things that can be done such as what Greg mentions, lowering the gearing. Also, you can declutch the supercharger and bypass it so that the engine behaves again like a 3.8L, but that has a lower gearing. NOW you can gain economy. But, it takes details like that that can make something like this work. The supercharger alone "with no other changes" LOWERS economy.
RE: Downsized charged engines, peak cylinder pressures?
from your logic you are failing to comprehend the dynamics of a running engine, fuel consumption is not linear to engine size, there are thousands of 350+ cubic inch engines that better 31mpg in a 3800lb vehicle, yet there are thousands more 4 cylinder and 6 cylinder engines less than 200 cubic inches that cannot match that fuel economy in even lighter vehicles
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
for example, lets say we have a 9:1 static compression ratio engine boosted making 18lbs of boost (which will return twice the horsepower the engine makes naturally aspirated), lets say this hypothetical engine reaches MBT at 36 degrees of timing at maximum pumping capacity, at 18lbs of boost we can only safely run 25 degrees of timing with the same 93 octane gasoline, the engine should return 320hp and 640hp respectively.
Now lets say we run that same engine on 87 octane gasoline, at maximum pumping capacity we can only push 28 degrees, anymore and the engine starts detonating, at 18lbs of boost we can only safely run 17 degrees of timing, the engine should return 280hp and 560hp respectively.
the octane rating of the fuel is its resistance to burning, by increasing the resistance you can run more ignition timing without detonation. A faster burning fuel can not run as much ignition timing.
disagree and you are wrong just like your text book
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
Just because you can control detonation (up to a point) by retarding ignition timing to later than MBT doesn't mean it solves all of your problems. The right solution is to run ignition timing close to MBT with minimum retard for detonation control, and use the octane rating that the engine wants!
By the way, I own and occasionally race a street-legal vehicle with a port-injected spark-ignition engine, non-turbo, that has high-13's compression ratio (it's not stock). I'm uncomfortable using any less than 94 octane, and when it goes to the drag strip, racing fuel. Retarding the ignition timing to try to make it run on regular is NOT happening. I prefer having the exhaust valves stay together and the coolant and oil temperatures stay in an acceptable range.
Some modern direct-injection engines, notably Mazda SkyActiv, are handling this by careful control of the spray pattern and careful design of the combustion chamber so that detonation either does not occur or remains manageable. Mine is not that sophisticated. Those engines are something of a halfway-house between gasoline and diesel engines - and Mazda is not using turbocharging in those (yet).
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
the amount of heat required to split an exhaust valve is significant, it will take a significant amount of retard to do so not to mention the engine will have to maintain that load for an extended period of time, the only real concern you have for damaged exhaust valves are in truck applications that see heavy loads during towing for extended periods of time, otherwise its null and not even worth mentioning
brian your 13:1 SCR engine shouldn't be ran on anything less than high octane fuel, but its not typical for a gasoline engine with that much compression to be turbocharged, in fact, the upper limit for boosting that i recommend is 10:1 unless you have direct injection which allows you to go higher safely
in any case, you just reiterated what i stated previously, you CAN run your engine with a lower octane fuel but it will require you to pull timing, it IS NOT required that you run higher octane fuel but you do so for safety, regardless of the fuel octane you run, you can typically reach MBT below approx 25% VE then thats when you wreak the benefits of the higher octane
i don't recommend you run your engine with low octane fuel, im just stating that you can
i've ran 450+ rwhp supercharged engines on 87 octane fuel with over 16lbs of boost
RE: Downsized charged engines, peak cylinder pressures?
Assess Statistical Significance
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
However, using the on-board fuel economy gauge to calibrate fuel use instead of a professional rig or at least calibrating the gauge or the pulse width vs amount injected and then thinking you have certifiable data to support extraordinary claims would be naive. Besides, the firm claim is that there were NO changes, so NO larger injectors.
On the other hand, applying substantial supercharging without changing injectors in several hundred cases would also seem incompetent. The risk is leaning out the engine under high power leading to catastrophic damage -guaranteed to happen in at least some of the hundreds.
RE: Downsized charged engines, peak cylinder pressures?
Tekton
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
Peak cylinder pressures are in the region of 120 Bar.
Reading Race Engine Technology this month, Mahle have said peak cylinder pressures for the new F1 engines next season are seeing peak cylinder pressures of 200 bar, and are running in knock conditions.
RE: Downsized charged engines, peak cylinder pressures?
The emphatic claim by decipha of better economy in ALL installations would be more credible if he gave full details of what he did. To be thorough in making such a claim (that overturns the textbooks and the science to date on vehicle fuel economy) decipha had to have done calibration runs on roads, before and after, on each vehicle. These runs, if properly done, would not have relied on the unverified reporting of the vehicles' internal gauges. Such a procedure would have been extraordinarily expensive for the installers and burdensome in time on the customers. Short of that, dyno runs would give an inferior estimate and had to have external fuel use measuring or a recalibration of the internal mpg meter. Again, this is not an inexpensive procedure tacked onto the cost of the installation.
For these reasons, LateApexEE's observation is tantalizingly suggestive of a VERY easy mistake. On the other hand, decipha is clear that he did not change injectors "no other changes".
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?
RE: Downsized charged engines, peak cylinder pressures?