Whats a waste gate for

[StianM]

Originally Posted by Carioca

Current state-of-the-art diesels achieve a similar result with VGT (variable geometry turbine).

They are more expensive and nead to be replaced twice as often.
No thanks!

Originally Posted by Frosty

Hello hello-- whats that? ---call mayday???

I think moust engines is with electronic boxes are only controled by them, if the electronics fail they will still runn.

If the car is striken by lightning the curent will just folow the steel chasi and to the ground and the same for a boat I asume.

As for electronic injection I think that is another thing just for engines running on a wide rpm and load range, the big two-strokes from B&W and Sulzer still use mecanical and they are 50% energy efficiant.

Convert mecanical energy into electrc and then convert it into mecanical again in a injector don't seam that eficiant to me. Bether to use the mecanical to open the injectors in the first place.

[Frosty]

[QUOTE=StianM;144648N


I think moust engines is with electronic boxes are only controled by them, if the electronics fail they will still runn.[ END QUOTE

Common rail injection, the fuel is pressurised and released by electronicaly controlled injectors.

Wont run without injectors.

When boat gets zapped by lighteneing it can take out everything from batteries to wind instruments.

It doesnt even need a direct hit.

Ive heard of some guys keeping sensative electronics in lead boxes while not in use. I dont know if that works.

[Steve in SoCal]

Well this has really transgressed; electronic engines are great when they run and dead in the water when they don't. Carrying spare parts is a must but that is true will all engines even the basic ones. The likelihood of a lightning strike taking out the engine controls is about how well the boat is rigged. If the engines were hit directly I can see the issue but hiding under a deck in an engine room it would have to be a hell of a strike. I have flow an airplane that has been hit by lightning and it did not fall out of the sky and it had electronic engine controls.

Jack or Frosty as you seem to have changed monikers. You sound like the engine for you is a Detroit 6-92 all mechanical blowers and turbos to delight your senses and it will survive a nuke bomb with air start. I would prefer a C15 or 3406E with all that electronic junk any day. The salt air is a concern but it is not a major issue in a well vented engine room.

Steve

[Frosty]

Well thats the trouble with lightening it just wont do as its told it gets all over the place for no reason. Fuzzy little black boxes just dont like it. It wont work!! --you cant open it , even to see if its fried .

Where money doesnt really matter the quickest way to get a boat on the way is a whole loom and all boxes. Less time than guessing.

When you being payed to do a job, do it. Doesnt matter how much it cost.

You can play with the old stuff later. Just get that boat moving and those stabalizers on.

Detroits? is that the 2 stroke crap.

I would like a Gardener with all removable injector pump simpley bolted to the side of the engine hooked up with a drive from the timing assy.

You could set that on fire and it would keep running. Whats to stop it.

Air start --Ok but Inertia starts as a back up

[sziane]

Hi Guys! I'm stuart. I am a marine engineer and I can tell you all you need to know about turbocharging (er, I hope!)

To put it simply, turbocharging is a process by which you increase the mass of air (oxygen!) in the cylinder in order to burn more fuel and therefore develop more power for the same sized cylinder. Thus, you increase the volumetric efficiency of the engine. Without a wastegate, the amount of boost that a turbocharger creates varies with the pressure of the engine's exhaust. This happens because exhaust pressure varies with relation to the engine's speed. This implies that as an engine reaches higher RPM's, increasing amounts of boost will be created by the turbocharger. The problem with this is that an engine can only accomodate a given amount of boost. Most engines are only meant to take about 4 bar if not less. In order to regulate the amount of boost that comes into the engine, a wastegate acts as a type of relief valve allowing a regulated amount of exhaust gas to the turbocharger's exhaust turbine. Once the engine starts producing more exhaust pressure then the wastegate system will allow, a flap is opened to redirect excess exhaust away from the turbine blades. In turn, this is where a wastegate gets it's name. It's a gate to carry away waste. In order to regulate when a wastegate opens, a boost conroller can be used.

There are two types of wastegates. One is known as a dump valve, although it's correct name is a blow-off valve, and this vents the waste gas to atmosphere. The other type is the diverter valve, and this diverts the waste gas to the inlet manifold or exhaust manifold. This varies with the engine. I hope this is clearer now. By the way, with larger engines, two (sometimes more) turbochargers are used, either at the same time or in a multistage turbocharging system in order to achieve the boost pressure instead of a large turbocharger. This is because the smaller turbos have less inertia and are more responsive to changes in load.

[sziane]

sorry, did I post this reply on the wrong forum??

[sziane]

Hi Guys! I'm stuart. I am a marine engineer and I can tell you all you need to know about turbocharging (er, I hope!)

To put it simply, turbocharging is a process by which you increase the mass of air (oxygen!) in the cylinder in order to burn more fuel and therefore develop more power for the same sized cylinder. Thus, you increase the volumetric efficiency of the engine. Without a wastegate, the amount of boost that a turbocharger creates varies with the pressure of the engine's exhaust. This happens because exhaust pressure varies with relation to the engine's speed. This implies that as an engine reaches higher RPM's, increasing amounts of boost will be created by the turbocharger. The problem with this is that an engine can only accomodate a given amount of boost. Most engines are only meant to take about 4 bar if not less. In order to regulate the amount of boost that comes into the engine, a wastegate acts as a type of relief valve allowing a regulated amount of exhaust gas to the turbocharger's exhaust turbine. Once the engine starts producing more exhaust pressure then the wastegate system will allow, a flap is opened to redirect excess exhaust away from the turbine blades. In turn, this is where a wastegate gets it's name. It's a gate to carry away waste. In order to regulate when a wastegate opens, a boost conroller can be used.

There are two types of wastegates. One is known as a dump valve, although it's correct name is a blow-off valve, and this vents the waste gas to atmosphere. The other type is the diverter valve, and this diverts the waste gas to the inlet manifold or exhaust manifold. This varies with the engine. I hope this is clearer now. By the way, with larger engines, two (sometimes more) turbochargers are used, either at the same time or in a multistage turbocharging system in order to achieve the boost pressure instead of a large turbocharger. This is because the smaller turbos have less inertia and are more responsive to changes in load.

[Carioca]

Originally Posted by sziane

........ This happens because exhaust pressure varies with relation to the engine's speed. This implies that as an engine reaches higher RPM's, increasing amounts of boost will be created by the turbocharger. .............

I suggest complementing with the above with:

"This happens because exhaust pressure varies with relation to the engine's speed and load. This implies that as a loaded engine reaches higher RPM's, increasing amounts of boost will be created by the turbocharger"

On no-load, there will obviously be some extra boost at higher RPM than at idle, and this may actually cause the boost gauge needle to budge momentarily as you rev the engin.

In contrast, the on-load picture changes substantially. The needle on the boost gauge begins to move up in a steady fashion.

[Frosty]

We know all this.

The thing is that in a boat you are standing there with the throttle lever in your hand or in a truck -under your boot. If you start to make too much power or the boost is too much back off with the throttle.

The only reason you need a waste gate is on a generator that has power coming on and off and it could run away.

[Mikefleetwood]

I have watched this thread with interest.

I would beg to differ with some earlier comments. I agree that as "driver" you have direct control of the throttle lever/pedal, but you do not have any control over what the turbo is doing. If you close the throttle, in response to changing demand, the reduction in fuel supplied (diesel) is instant, however, the turbo has considerable inertia and will generate air pressure considerably in excess of that needed for combustion for some time as it slows down. The reason for the waste gate is to get rid of this excess pressure safely.

In a petrol engine, depending on where the waste gate is positioned, this can result in fuel/air mix being dumped into the hot exhaust - watch a turbo-charged F1 car changing down and you will see what I mean!

[Carioca]

Frosty,
You continue to ignore engine manufacturers´warranty concerns !

I am sure there are people out there with their eyes glued to the gauges on the dash and imbued with well developed senses (noise, smell etc).......but what if the chap has had a couple of drinks before climbing into his turbo-diesel and driving it away ?

You will be the last candidate to consider for a vacant position in Warranty Claims, unless you change your ways !


MikeFleetwood,
On a turbo-diesel with conventional fuel-injection (mechanical), activation of the waste-gate is tagged to boost-pressure, period. Have you seen the aneroid sensor-bulb and the activation arm used on such turbos ?

So if you are, say, at part-load and then suddenly ease off on the throttle, you are still a long shot away from the boost-pressure level that activates the waste-gate ( the latter level is a full-load boost-pressure)

You are right in affirming that boost-pressure at part-load will not drop off immediately on easing off on the throttle, because of the inertia involved. But the load on the drive-train will soon make its effect show on the engine, the latter´s RPM will begin to drop........fuel will corespondingly tail-off too....

I will hazard a guess on the example presented regarding F-1 petrol-engine cars, but as exhaust temperatures (and manifold temps) are much higher than in diesels - what makes the diesel more efficient ? - any unburnt excess fuel present in the exhaust charge during the throttle-off transient, may combust. Keep in mind too that petrol fuel is volatile, diesel is not.

In fact on a diesel engine with diesel as a pilot charge to intiate combustion in the cylinder and air charged with propane/natural gas as the main fuel inducted into the intake manifold, I would not be surprised if a flame showed up in the exhaust piping on easing-off the throttle.

[mr curious]

before messing with a turbos performance, you should have 2 essential gauges, a pyrometer and a boost gauge.