Explain water injection

[Shortround6]

The use of water in jet engines was for a different purpose or perhaps better stated as a different method of achieving the same purpose, that is more power
However in the jet/s it was help cool the combustion chamber/s and turbine and faded from use when better combustion chamber materials and design become available and when better turbine blade material and cooling methods also became available.
It was used in some early jets like it was used in Piston engines, to increase the density of the air flowing through the compressor but since jets are not really subject to detonation that reason for using it was out.

In jets the major limit to more power for brief periods of time was turbine temperature, monitored by jet pipe or exhaust gas temperature.
cooking the turbine blades could lead to catastrophic failure very quickly.

In piston engines it was detonation in the cylinders which could lead to either mechanical failure parts stretching, bending, breaking and departing the engine at high speed) or local over heating, few pistons actually melt from the average temperature in the combustion chamber but once pre-ignition or low grade detonation sets in the meeting of flame fronts inside the combustion chamber can lead to localized hot spots well above the average "high" or peak temperature in a properly running engine. Then you get holes in pistons and other meltdowns.

I would also note that in some cases it is easier to use an "internal" coolant ( water injection, excess fuel) than redesign the cooling system of an existing engine. Change the amount of fin area on an air cooled engine or change the water passages in a liquid cooled engine, or pump volume or change oil system to handle more heat.

I would note that the using excess fuel method was known and used in WW I on air cooled Renault V-8 engines and their derivatives which were known for horrible fuel consumption and almost glow in the dark cylinder heads

 

[Ascent]

Increasing the mass flow through a gas turbine will increase the thrust.

The amount of thrust an engine gives you is the air mass it moves multiplied by the amount it accelerates it by. If you increase the mass you automatically increase the thrust. How much actual effect this will have I don't know, but it will make a difference.

 

[YF12A]

Ok, I'm date stamping myself but here goes. Anyone remember the Oldsmobile Jetfire from the early '60's that was a turbocharged V-8 with a water/alcohol tank that owners didn't understand and would run dry? To be fair, the whole package was not really well thought out.

My favorite "fun" fuel was nitro-methane. In a Top Fuel engine, get the mixture wrong and the engine would, as NASA said of an unhappy rocket engine, suffer a " catastrophic disassembly ".

 

[Peter Gunn]

Ok, I'm date stamping myself but here goes. Anyone remember the Oldsmobile Jetfire from the early '60's that was a turbocharged V-8 with a water/alcohol tank that owners didn't understand and would run dry? To be fair, the whole package was not really well thought out.

My favorite "fun" fuel was nitro-methane. In a Top Fuel engine, get the mixture wrong and the engine would, as NASA said of an unhappy rocket engine, suffer a " catastrophic disassembly ".

Boost Beginnings: The Turbo Jetfire - Speedhunters

 

[Balljoint]

Ok, I'm date stamping myself but here goes. Anyone remember the Oldsmobile Jetfire from the early '60's that was a turbocharged V-8 with a water/alcohol tank that owners didn't understand and would run dry? To be fair, the whole package was not really well thought out.

My favorite "fun" fuel was nitro-methane. In a Top Fuel engine, get the mixture wrong and the engine would, as NASA said of an unhappy rocket engine, suffer a " catastrophic disassembly ".

Glow plug model airplane fuel was high in nitro. One can in a full tank of gas with a little luck would at least make the exhaust of a flathead V-8 bark.

 

[Koopernic]

Ok, I'm date stamping myself but here goes. Anyone remember the Oldsmobile Jetfire from the early '60's that was a turbocharged V-8 with a water/alcohol tank that owners didn't understand and would run dry? To be fair, the whole package was not really well thought out.

My favorite "fun" fuel was nitro-methane. In a Top Fuel engine, get the mixture wrong and the engine would, as NASA said of an unhappy rocket engine, suffer a " catastrophic disassembly ".

Water Injection might have a positive effect on pollutants, especially NOX emissions on turbo supercharged cars. I properly integrated turbosupercharger is more efficient and produces less pollutants than a similarly powerful normally aspirated engine. Adding Water Injection might be a way of increasing power while reducing pollution. Diesels are turning up equipped with the SCR selective Catalytic Reduction which works via a ammonia or urea addition from a small tank meant to last a service interval. Adding water in a similar way to an Otto engine wouldn't be difficult so long as there was an inbuilt deionisation Filter.

 

[XBe02Drvr]

Increasing the mass flow through a gas turbine will increase the thrust.

The amount of thrust an engine gives you is the air mass it moves multiplied by the amount it accelerates it by. If you increase the mass you automatically increase the thrust. How much actual effect this will have I don't know, but it will make a difference.

I used to work on Fokker F-27s powered by RR Dart engines. These planes were borderline underpowered, especially in hill country with short runways and steep climb gradients. Without water-meth, departures could be pretty hairy. The increase in mass flow without a rise in EGT gave up to 20% increase in ESHP. Judging by the quantities of W/M we pumped into those planes, the crews apparently thought most of their takeoffs were "hairy". A lot of the time, takeoffs were payload limited, and W/M would save two or three revenue pax from being DBd.
Boy those Darts could scream!
Cheers,
Wes

 

[BiffF15]

You gotta love those little Fokkers!

Cheers,
Biff

 

[XBe02Drvr]

You gotta love those little Fokkers!

Cheers,
Biff

Yup, brick sh!thouses with Model T engines, an electrical system courtesy of "The Prince of Darkness", and pneumatic wheel brakes like an 18 wheeler with ABS, but a sweet flier once you could peel her off the ground.
Cheers,
Wes

PS: And don't forget the drip pans that go under the nacelles; they're Limey engines after all! Fossils from the Paleozoic Era of turbine technology. We used to rotate the Darts through the RR overhaul shop at YUL, and at one point our newest bird (a 1976 model) had its OEM engine on the right side and a 1947 (first year of manufacture) Dart (62,000 hours TT and fresh out of overhaul) on the left. I was sent to look up something in the engine logbook, and was astounded to discover it ran to four volumes! Some wag promptly put a "Fred Flintstone" sticker on the nacelle, and I got stuck with getting it off.

 

[Todd Secrest]

So basically it works like Nitrous in a race car, correct? Lower the temperature, increase density, increase fuel in the combustion chamber.

Normal air is 20% oxygen, where as Nitrous (nitrogen oxide) is 33% oxygen.
So feeding Nitrous (instead of normal air) to a car engine gives the engine cylinders chambers more oxygen, allowing the fuel to burn longer or more completely, creating more cylinder pressure, giving more power.
Never heard that Ntirous lowers temperature in the air/fuel going into the cylinder (guessing it does not).
So using Nitrous does not add more fuel (gasoline) to the combustion chamber, just adds more oxygen to help the fuel burn more completely.

 

[XBe02Drvr]

Normal air is 20% oxygen, where as Nitrous (nitrogen oxide) is 33% oxygen.
So feeding Nitrous (instead of normal air) to a car engine gives the engine cylinders chambers more oxygen, allowing the fuel to burn longer or more completely, creating more cylinder pressure, giving more power.
Never heard that Ntirous lowers temperature in the air/fuel going into the cylinder (guessing it does not).
So using Nitrous does not add more fuel (gasoline) to the combustion chamber, just adds more oxygen to help the fuel burn more completely.

Yes, but if you're adding more available O2 and gaining more complete combustion, you're driving an already stressed engine toward a too-lean condition with the possible catastrophic consequences that entails. The antidote would be to richen the mixture, reducing charge temperature by atomization.
Cheers,
Wes

 

[Shortround6]

From Wiki:
Nitrous oxide is stored as a compressed liquid; the evaporation and expansion of liquid nitrous oxide in the intake manifold causes a large drop in intake charge temperature, resulting in a denser charge, further allowing more air/fuel mixture to enter the cylinder. Sometimes nitrous oxide is injected into (or prior to) the intake manifold, whereas other systems directly inject, right before the cylinder (direct port injection) to increase power."

Any compressed gas (especially if compressed to the point it is stored as a liquid) drops in temperature as it expands.

 

[Koopernic]

From Wiki:
Nitrous oxide is stored as a compressed liquid; the evaporation and expansion of liquid nitrous oxide in the intake manifold causes a large drop in intake charge temperature, resulting in a denser charge, further allowing more air/fuel mixture to enter the cylinder. Sometimes nitrous oxide is injected into (or prior to) the intake manifold, whereas other systems directly inject, right before the cylinder (direct port injection) to increase power."

Any compressed gas (especially if compressed to the point it is stored as a liquid) drops in temperature as it expands.

On the basis of NO₂ having a latent heat of vaporization of 300kJ/kg and air having a specific heat capacity of 0.7kj/kg per degree C then about 1kg of nitrous oxide should pull down 13kg of air by over 35 degrees Celsius or Kelvin. That should contract it by about 12%, in addition we've added oxygen. The lower temperature means more supercharger boost or compression ratio can be used and of course the more oxygen from both the greater quantity of air and the NO₂ itself means ore fuel can be burned.

 

[Todd Secrest]

From Wiki:
Nitrous oxide is stored as a compressed liquid; the evaporation and expansion of liquid nitrous oxide in the intake manifold causes a large drop in intake charge temperature, resulting in a denser charge, further allowing more air/fuel mixture to enter the cylinder. Sometimes nitrous oxide is injected into (or prior to) the intake manifold, whereas other systems directly inject, right before the cylinder (direct port injection) to increase power."

Any compressed gas (especially if compressed to the point it is stored as a liquid) drops in temperature as it expands.

COOL.

 

[Koopernic]

Ok, I'm date stamping myself but here goes. Anyone remember the Oldsmobile Jetfire from the early '60's that was a turbocharged V-8 with a water/alcohol tank that owners didn't understand and would run dry? To be fair, the whole package was not really well thought out.

My favorite "fun" fuel was nitro-methane. In a Top Fuel engine, get the mixture wrong and the engine would, as NASA said of an unhappy rocket engine, suffer a " catastrophic disassembly ".

I looked this car up on Wikipedia, fascinating. Very advanced for its day. with modern electronic control this would be much easier to implement today.

There was one other commercial vehicle that used water injection in the USA. That was the Rumley Oil Pull Kerosene tractors of the 1900s.

Kerosene became a desirable fuel for tractors when the motor car created a gasoline shortage and high petrol prices. Because Kerosene has a very low octane number of 25 it has to be used with low compression ratios of around 3.5 to 4 (unless used in a diesel cycle)

The Rumley ran a compression ratio of 5.5. They did this by having a water jet in the carburetor. It was placed ahead of the fuel jet so that the water was drawn in only at at high air flow rates when knocking was a danger. They were very reliable.

Model T Fords started out with a CR of about 4.5:1 and then dropped to about 4 and then 3.9 as gasoline quality fell. New refining techniques, thermal cracking helped.

 

[Koopernic]

actually the MW 50 was used at high altitudes in the AS 109's according to former pilots....

First hand knowledge should always be valued. Your old flyers were right.

Me 109G14A or ME 109G6AM could use MW50 to 11,000m/36,000ft and still gain 16kmh or 10mph.

Wikipedia.de gives some general information on MW50. It added about 100hp even without additional boost pressure, it added about 300hp with additional boost. The 115L tank on a Fw 190D9 gave 40 minutes of running so the addition rate of MW50 must have been only 1/3rd of the fuel flow rate.

Below a chart of a Me 109G14 speed at 1.3ata max boost versus 1.7 ata max boost with MW50 added to allow the additional boost.

You can see that above the full throttle height of 6600m (point speed falls of) where the supercharger is physically unable to supply more than 1.3 ata that MW50 is still supplying an extra 16kmh/10mph. This is due to the cooling effect making the air more dense.

The Me 109G14ASM of course would have benefited much more due to its larger supercharger. The 1.3ata full throttle height went from 6600m/22000ft to 8300m/27500 with the AS engine. Just above B17 altitude.

I suspect that if the aircraft ran out of MW50 they could revert to their previous 1.42ata emergency boost limit. What was needed for the Me 109 to compete with allied aircraft was the DB603L with 2 stage supercharger which could have maintained the 1.75ata to around 8 km.

This is a height in km versus speed in km/h chart for Me 109AM with MW50 at 1.7ata and without at 1.3ata.

 

[tomo pauk]

First hand knowledge should always be valued. Your old flyers were right.

Me 109G14A or ME 109G6AM could use MW50 to 11,000m/36,000ft and still gain 16kmh or 10mph.

Below a chart of a Me 109G14 speed at 1.3ata max boost versus 1.7 ata max boost with MW50 added to allow the additional boost.

On the DB 605AM working at 2800 rpm, the manifold pressure will decrease from 1.7 ata (available from SL to ~4.8 km with ram) to 1.42 ata (at 7000 m with ram) and will be further decreasing as the altitude goes up. With 2600 rpm, max manifold pressure was 1.30 ata, from SL to ~6.5 km (with ram), and decreassing above 6.5 km.
1.42 ata + 2800 rpm with water injection used will produce more power than same setting without water injection.

You can see that above the full throttle height of 6600m (point speed falls of) where the supercharger is physically unable to supply more than 1.3 ata that MW50 is still supplying an extra 16kmh/10mph. This is due to the cooling effect making the air more dense.

The extra 200 rpm and extra ~0.12 ata produces some 6-7% more power above 6.5 km (with ram), water injection provides also similar increase of power - thus extra speed.

The Me 109G14ASM of course would have benefited much more due to its larger supercharger. The 1.3ata full throttle height went from 6600m/22000ft to 8300m/27500 with the AS engine. Just above B17 altitude.

I suspect that if the aircraft ran out of MW50 they could revert to their previous 1.42ata emergency boost limit. What was needed for the Me 109 to compete with allied aircraft was the DB603L with 2 stage supercharger which could have maintained the 1.75ata to around 8 km.

This is a height in km versus speed in km/h chart for Me 109AM with MW50 at 1.7ata and without at 1.3ata.

2-stage supercharger of the DB 605L was delivering 1.75 ata up to 9.6 km, water injection was used for boosts of and above 1.43 ata. Intercooler was not used, CR was very high - 8.5:1 and 8.3:1.

 

[airminded88]

Nothing to add really except I remember the best explanation on water injection I got was from my freshman high school drafting teacher Mr. Delevanno who had been a Thunderbolt crew chief in the South Pacific during WWII. Excellent teacher, spent much time in his office talking aviation.

This thread for some reason stirred some great memories of a wonderful man, thanks.

That sounds like my type of teacher as well

 

[XBe02Drvr]

That sounds like my type of teacher as well

One of my teachers in mechanic school was a Korean War F86 pilot who spent 22 years flying everything from Texans to Globemasters. Held the record for four engine landings in the C124. Instructed for Mohawk airlines, then mech school, then Director of Training for Empire, Simulator Facility Manager for Piedmont and eventually USAIR. My kind of teacher.
Cheers,
Wes

 

[soulezoo]

One of my teachers in mechanic school was a Korean War F86 pilot who spent 22 years flying everything from Texans to Globemasters. Held the record for four engine landings in the C124. Instructed for Mohawk airlines, then mech school, then Director of Training for Empire, Simulator Facility Manager for Piedmont and eventually USAIR. My kind of teacher.
Cheers,
Wes

Old Shaky was a scary aircraft to fly and even be a passenger on.