1.6l V6 Turbo engine exhaust temperature

[gruntguru]

I doubt that an "even spread" of fuel is optimal.

IMO the optimum level of turbulence is applied to the air by port and chamber geometry and injection is a single event late in the compression stroke. The ideal would be a "cloud" of air-fuel mixture at lambda 1.0 to 1.2, surrounded by air (but still in contact with the spark gap). The overall AFR (including the "air blanket") - approximately 1.3 to 1.4.

I am not questioning you here, I'm just wondering why you think that is the best?
In my mind, the more evenly you heat up the gas volume inside the cylinder, the higher MIP you achieve and therefor also a higher end power. Now if the fuel that is to be combusted is more evenly spread around the cylinder the heat should distribute better to all of the gas volume in the cylinder.

The fuel injectors I work with are diesel injectors so I can't say much about a petrol direct injection engine but they (the diesel ones) have extremely small holes in them drilled evenly in a circle around the injector in various angles and height, leading to as even distribution as is possible... but since the injection pump is mechanical and not a common rail system with a solenoid valve (or some other form of controllable valve) there is only one injection pulse.

1. You certainly do need a "connected" path of evenly distributed air-fuel for the flame front to quickly spread through the entire mix.
2. From a pressure standpoint it doesn't much matter if some gas gets hotter than others - the available heat will produce a similar cylinder pressure rise whether evenly distributed or not.
3. Cooler gas (fresh air) at the periphery of the chamber will reduce heat loss to the walls.
4. Fresh air at the periphery will avoid flame quenching and unburned fuel which normally occurs at the walls.
5. Fresh air at the periphery reduces the distance the flame has to travel and therefore reduce combustion time.
6. Fresh air at the periphery reduces the likelihood of knocking for the same reason.

Multiple pulses in a common rail diesel come in two kinds.

1. Very early (large) pulses designed to create a pre-mixed region for later ignition (and SI-like combustion via flame front propagation) by the main injection event. (Look for research by Bengt Johannson)
2. Early (short) pulses designed to reduce ignition delay of the main pulse which causes "Diesel knock" as follows.

Diesel Knock When fuel is injected there is a delay before ignition occurs. During this delay period, a significant quatity of fuel may have been injected, which could burn rapidly (almost simultaneously) causing a shock wave similar to detonation in SI engines. Usually not harmful, but causes the typical diesel-knock noise which can be annoying.

[Wayne DR]

If you look at the arrangement then I think you can say that the Mercedes was running their turbo hotter than others (I still think that is part of their advantage). Probably Honda copied that strategy, so 1000 degrees seems possible, although because of material limitations I don't see how they can get much hotter than that.

For the other engine builders I don't know. Last year they seemed to run their turbos colder but I don't know what they have done for this year.

I was quoting temperatures post turbo, in the single 4-6" dump pipe (I don't imagine they would use exotics for this). Exhaust gas temperatures in the headers will still be over 900 degrees C.


The turbine-MGU-H uses what I would describe as a Brayton Cycle to turn waste heat and pressure (not used by the compressor) into electrical energy. The rules don't limit the amount of this energy that can be directly fed to the MGU-K. My guess is that Mercedes are continually harvesting between 75-100kW in this way (Sustainable mode). (This is the main area that Renault and Ferrari were behind in last year)

As a side note, I would be interested to see if Ferrari are still running their "Push to pass" mode from last year, where the driver can open a damper to allow the exhaust gases bypass the turbine completely and run the compressor off 100% electric power.

[gruntguru]

+1
To clarify. It is not thermodynamically desirable to increase exhaust temperature from the piston engine for the purpose of increasing turbine power. Generally, any increase in piston engine EGT is accompanied by a reduction in thermal efficiency (and therfore crankshaft power under fuel-flow-limited regulations). Of course whatever EGT exists, should be maintained all the way to the turbine using insulation, minimising manifold surface area etc.

[Cold Fussion]

As a side note, I would be interested to see if Ferrari are still running their "Push to pass" mode from last year, where the driver can open a damper to allow the exhaust gases bypass the turbine completely and run the compressor off 100% electric power.

Wouldn't all 4 engines have this mode of operation? If you have an electrically controlled waste gate then this mode only a slight software change.

[Wayne DR]

Wouldn't all 4 engines have this mode of operation? If you have an electrically controlled waste gate then this mode only a slight software change.

Normally with a waste gate, you are not concerned about the pressure drop over the system. The Ferrari design appeared to be able to be a manually controlled full size (i.e. full flow and low pressure loss) butterfly damper with full size pipes per bank. You can see photos of the exhaust system from the items auctioned off by Marussia (Manor) earlier this year.

[riff_raff]

+1
To clarify. It is not thermodynamically desirable to increase exhaust temperature from the piston engine for the purpose of increasing turbine power. Generally, any increase in piston engine EGT is accompanied by a reduction in thermal efficiency (and therfore crankshaft power under fuel-flow-limited regulations). Of course whatever EGT exists, should be maintained all the way to the turbine using insulation, minimising manifold surface area etc.

Good point, and this is true with most IC engines. A higher EGT would mostly indicate that there was less expansion of the exhaust gas being done in the cylinder. Using the piston to extract work from the combustion gas is usually more efficient than using an exhaust turbine to do the same work.

[Edis]

@gruntguru: I get why the compression ration needs to be lowered when running a turbo with a port injection system, but why does this need to happen in a direction injection engine as well? I'm studying on GDI right now and din't find an actual reason so far. My thinking is that the ability to time the fuel injection would significantly reduce any chance of the mixture pre-detonating.

Thanks!

this is something that has intrigued me about the new engines, just when in a cycle do they inject the fuel? there are so many different options here.
if you inject during the intake stroke, you should get a better and more even mixture, but you will still have the problems of pre-ignition so the compression ratio will still need to be lowered.
if you inject during the compression stroke you run the risk of spontaneous ignition if the temperatures in the cylinder are high enough.
if you inject at the point of ignition, you run the risk of an uneven mixture, though if you get it right you can use a stratified charge to try and achieve better efficiency.

With road car engines you typically use different modes at different loads and speeds, which requires different injection timings. At low load and speed you typically use stratified combustion, which require injection during the late compression stroke. The purpose of the stratified mode is to create a slightly rich fuel mixture around the spark plug, with air around it. To achieve that fuel mixture around the spark plug you typically use either wall guided, air guided or spray guided injection.

At higher speeds and loads the engine will switch to a homogeneous mode. Some engines will have different homogeneous modes, like a lean homogeneous, a stoichiometric homogeneous, and a rich homogeneous mode. During homogeneous modes the injection is done during the intake stroke, typically after the exhaust valves have closed to prevent fuel loss to the exhaust system.

Previous racing engines using gasoline direct injection have typically only used the homogeneous modes, with stratified mode being limited to low loads and speeds there hasn't been much use of it in racing. The question is, up to what speeds and loads are stratified modes possible to use?

I would have guessed between 580 and 640 deg C varying with turbine efficiency. (The lower the temperature, the higher the MGU-H output is).

This is somewhat supported by the heat tint (temper) colour of the Ferrari turbo dump pipe of blue/dark blue (shown in photos from this weekend).

Colour - Temp (deg C)
pale yellow - 290
straw yellow - 340
dark yellow - 370
brown - 390
purple brown - 420
dark purple - 450
blue - 540
dark blue - 600

You have to watch out with these colors. These are for steel. The color is originating from thin film interference on the oxide scale that forms on the metal. Your basically looking at the thickness of the oxide scale. The exhaust systems likely are made from a superalloy like inconel which is much more oxidation resistant and thus give a wrong indication.

I don't know for these ICE's but for the old V8 engines I would guess that the temperature is 900C-1000 at the manifold. If you see them on the dyno you can see the exhaust appears translucent (it is not really translucent but you get these weird cold shadowing effects). That happens in this temperature range.

http://s1.cdn.autoevolution.com/images/ ... 1704-7.jpg

The temperature then drops off. It is clear from the Mercedes picures that they go to greath lengths to insulate their exhaust so they will experience very little drop-off.
http://encdn.f1i.com/wp-content/uploads ... aust-2.jpg

Last year Renault and Ferrari had their exhaust unshielded so there the temperature loss will be much greater. Don't know if that is still the case.
http://www.racecar-engineering.com/wp-c ... maruuu.jpg

If you look at the arrangement then I think you can say that the Mercedes was running their turbo hotter than others (I still think that is part of their advantage). Probably Honda copied that strategy, so 1000 degrees seems possible, although because of material limitations I don't see how they can get much hotter than that.

For the other engine builders I don't know. Last year they seemed to run their turbos colder but I don't know what they have done for this year.

The red glow of the exhaust manifold of that Mercedes engine would indicate that the manifold itself has a surface temperature of roughly 600 degrees. At 700 degrees it would be a lot brighter, and slightly orange in colour. The dark areas of the manifold are certainly below 500 deg C.

The exhaust gas in the manifold is obviously hotter than the surface of the exhaust manifold.

+1
To clarify. It is not thermodynamically desirable to increase exhaust temperature from the piston engine for the purpose of increasing turbine power. Generally, any increase in piston engine EGT is accompanied by a reduction in thermal efficiency (and therfore crankshaft power under fuel-flow-limited regulations). Of course whatever EGT exists, should be maintained all the way to the turbine using insulation, minimising manifold surface area etc.

Good point, and this is true with most IC engines. A higher EGT would mostly indicate that there was less expansion of the exhaust gas being done in the cylinder. Using the piston to extract work from the combustion gas is usually more efficient than using an exhaust turbine to do the same work.

With turbocharged SI engines knock tend to cause a bit of trouble here, since increasing expansion usually means higher peak firing pressures. Either by compression ratio or by ignition advance.