These days nearly every engine is fuel injected so the fuel will be introduced after the turbo, either in the intake manifold in the case of port injection or into the combustion chamber in the case of gasoline direct injection or diesel. Back in the bad old days of carburetors, most of the turbo applications were "suck through" which meant that the carb was up stream of the turbo. The alternative was a "blow through" carb which meant it was pressurized when under boost. This greatly complicated the plumbing and required a higher pressure fuel pump with a complicated pressure regulator.

No idea what you mean by "gas generator".

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Here's a schematic.

https://www.researchgate.net/profile/Anh_Tu_Nguyen...

After studying this, what remaining questions do you have?

I don't quite understand what you mean by "gas".

If by "gas" you mean "gasoline" as used in any normal automobile, nowadays they have multi-point fuel injection with an electrically operated injector at each intake port (sometimes directly into the cylinder), which is completely unaffected by the engine being turbocharged. The gasoline is sprayed in as a liquid into either each cylinder's intake port or directly into each cylinder, depending on the design of the particular engine under study.

If by "gas" you mean "natural gas", gaseous fuel, methane+ethane, I don't have experience with them but you can be certain that it is injected into the intake system under pressure after the turbocharger and intercooler, perhaps in the vicinity of the throttle (could be before or after), or perhaps into each intake port in the same manner as is done with port-injected gasoline engines.

Mixing fuel with air before the turbo compressor results in having a rather large volume of already-mixed air and fuel ready to produce a rather substantial explosion in the event that the engine has a backfire into the intake system. It can be done this way, and it certainly has been done this way, but it isn't the preferred way to do it.

From your description I am assuming you are speaking of the common low pressure gaseous (natural gas, propane, etc gaseous-PHASE) fuel used on generators large and small alike. Typically "gas" is injected at a single point just inside or slightly downstream of the air cleaner housing via a "mixer" (typically needle or annulus) which commonly does a poor job of mixing the fuel and air. Turbos can and do improve the mixing significantly, however the best mixer in the system is typically the combustion chamber itself, nothing like the heterogeneous mixture hitting the piston to mix things up a bit.

While these systems are great for generators, pumps, and other stationary engines running at a fairly constant speed and load, the downside of these systems is that they are rather slow to react to large changes in speed and load. When a large change is necessary, the engine basically has to swallow the entire air system's volume of mixture which equals significantly more revolutions of the engine (read: time) than a port or direct injected system with the fuel admission site closer to the cylinder. There are less common gaseous port and direct injected systems commercially produced today but these are usually a necessity of CNG/LNG/propane vehicles and an unnecessary cost for stationary engines.

Ah thanks, I've never worked on stationary power units big enough to contain a turbocharger.

At least in the automotive size range, there are a couple of additional terms that are useful.

A "draw-through" arrangement has the fuel mixing and throttling apparatus (usually a carburetor) upstream of the turbo compressor. The entire volume of the turbo compressor and intake manifold and the ducts that connect them are thus filled with already-mixed fuel and air. If one wants decent throttle response, this generally means not having an intercooler (which would add system volume). I don't know if a draw-through has ever existed with an intercooler, maybe it has and I'm not aware of it. Another consequence is that when the engine is running at partial load, the seal in the turbocompressor is under vacuum because of the intake manifold vacuum (which presents its own set of issues, because usually these are non-contact seals that rely on the turbocompressor being designed such that the seal is always under positive pressure, i.e. any leaks are in the direction of leaking compression pressure into the crankcase as opposed to drawing oil into the intake stream).

A "blow-through" arrangement has the fuel mixing and throttling apparatus downstream of the turbo compressor, operating under boost pressure. The turbo compressor and all of the ducts and other components (potentially including an intercooler) contain air only.

In automotive applications, all current implementations are blow-through due to the need for using multipoint fuel injection for emission control reasons.

Draw-through has been used in the past (with carburetors, before fuel injection became universal).

I cannot speak for what has been done with stationary or heavy-truck applications that operate on gaseous fuel ... CWB1's post suggests that these can be draw-through.

@ Brain Peterson

The picture does not show the injection point of a Fuel so the remaining question is my asked question??

Very much thanks to all Guys.

I am talking about natural gas. I have Jenbacher 320 and 420 engines fir which I am told that gas is mixing with air and after turbo charger it is injecting into combustion chamber of which I am totally in doubt?

I am not the slightest bit familiar with that engine, but a google image search quickly found pictures of the cylinder head, and the bottom face of the cylinder head has an intake valve, an exhaust valve, and a spark plug ... so it is not direct-injection.

Beyond that ... brief searching did not turn up a conclusive answer to your question, but it appears that you have something available that I do not ... the engine itself! Go over to where it is, find the pipe where natural gas comes into the area, and follow that pipe! If it eventually goes into the air inlet before the turbocharger inlet, it is draw-through. If it goes in after the turbocharger outlet but before the intake manifold, it is blow-through single-point injection. If it goes into another manifold that in turn splits off with a pipe to each cylinder, it is multi-point injection.

A large number of larger industrial natural gas (and similar fuels like propane and methane) use a fuel system that induces fuel gas at the turbocharger inlet.

Older designs used mixers or carburators in the air cleaner housings, all newer designs use a fuel management system controlled by the engine ECM, such as a Woodward Raptor or TechJet valve.

The primary driver of moving the fuel introduction into the inlet side of the turbo was because of the limited availablity of higher pressure fuel gas at the point of use to overcome the engine's manifold pressure on larger low emissions turbocharged engines. Especially in Europe where fuel gas pressure distribution pressures are regulated to lower levels. Also as biogas type fuels became more commonly used, such as digester or landfill gas, the cost of increasing fuel gas pressure to the engine became prohibitive and many manufacturers were driven to using low fuel gas pressure designs.

A typical natural gas engine with a conventional design, fuel gas introduced after the turbo requires fuel gas supply pressures of 30-70 PSI for many engines. Most low fuel gas pressure arrangements require 2-5 PSI fuel gas supply pressure.

Jenbacher, Caterpillar, Cummins, MWM and many other manufacturers all provide low fuel gas pressure system on many of their engine models, most use the same fuel control hardware.

Hope that answers your question.
MikeL.

Mike what's used to create Low or High pressure gas from digester type sources? Some sort of computer controlled compressor or ??

Keith Cress
kcress - http://www.flaminsystems.com

Digester gas systems usually are a couple of steps, a blower pulls methane off the digester at anywhere from .5 to 2 psi, and in most cases goes to an initial cleaning stage, mostly solids and water removal. Then it is compressed again and goes to a more extensive cleaning stage, depending on what contaminants are in the gas. If the gas is fairly "sweet" it may just go thru a chiller to get as much of the water out as it can, then filtered. If the gas is "sour" usually high H2S or other compounds, then it can go thru a fairly complex cleaning process, the more complex the process, usually the higher pressure required to push it thru.

Depending on the engine fuel system design it can either go directly to the engine or to a booster compressor, then to the engine.

Most gas compression skids I get around are PLC controlled, usually tied in some way to an overall plant SCADA for monitoring and control. In some areas, mostly California but others as well, fuel treatment and pressure are now required to be monitored and datalogged for emissions record keeping.

Here is a link to a company that specializes in gas systems, https://www.glauber.com/markets/renewable-natural-... There are others as well, but their website gives a pretty m=nice summary of what goes into a system for biogas recovery for RICE use.

Hope that helps, MikeL.

My understanding of the terms "blow through" and "draw through" has always been a reference to the throttle plate location - not the fuel addition location. For example, I am currently designing a "draw through" turbo installation on a port injected 4 cylinder car. The injectors will remain in the ports, downstream of the compressor but the throttle plate will be upstream of the compressor. Throttle location has far more impact on the function of the system than whether the fuel is admitted pre or post compressor.

je suis charlie

I found a GE PDF file for a larger Jenbacher type 6 but they seem to use the same technology across all the families. It says:

Air / fuel mixture charging
Fuel gas and combustion air are mixed at low pressure before entering the turbocharger
Main gas supply with low gas pressure, mixture homogenized in the turbocharger

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Thanks Mike.

Keith Cress
kcress - http://www.flaminsystems.com

Quote:

Throttle location has far more impact on the function of the system than whether the fuel is admitted pre or post compressor.

That depends on the air system and engine arrangement. For reasonably compact automotive engines I'd tend to agree, but industrial engines are often 12-20+ cylinders,the air system is many feet long, and its common to deal with only a couple fuel admission points far upstream of the cylinder. In those cases fuel mixing and cylinder-cylinder distribution is critical, the throttle meanwhile is pretending its the tiny rudder on the Titanic.

When I worked daily in that world it wasn't uncommon to fire up a test mule built from spare parts to find a 20% fueling difference between the front and rear cylinders bc a diesel intake manifold had accidentally been used on a gaseous engine, gaseous systems typically being built on an existing diesel's architecture and the diesel manifold obviously not designed for optimum cylinder-cylinder fuel distribution.

Thanks all for such knowledgeable posts.

I work on the Waukesha Engines, Jenbacher and Waukesha is now owned by Innio,

On all the Waukesha Engines I have work on and to my understanding of Natural Gas Engines, you have Carburetor that mixes your air and fuel, this is either
an Impco or Deltec carb. In either case, it is common that first, the Air and fuel is mixed, then compressed (by turbo charger) then cooled by Inter cooler, then it is
regulated through some sort of throttle body and then it enters an intake manifold.

This concept is known as drawthrough carburation. It has the of advantage that you can run a fairly low Fuel pressure to your engine and is more likely used on Lean Burn Engines.

Quote:

If by "gas" you mean "gasoline" as used in any normal automobile, nowadays they have multi-point fuel injection with an electrically operated injector at each intake port (sometimes directly into the cylinder), which is completely unaffected by the engine being turbocharged.

This isn't exactly true. You have to maintain the pressure delta across the injectors to not affect their operation. You have to increase the fuel pressure by 1 bar if you're boosting at 1 bar to maintain the same injector flow rate.

Even more interesting. What LionelHutz says is true - for liquid fuel. For gaseous fuel at pressures high enough to create choked flo conditions in the injector nozzle (approx 2 x manifold pressure or higher) the injector flow is independent of back-pressure (MAP) so fuel pressure needs to be held constant.

je suis charlie

Agreed with both of the above although these days with returnless liquid fuel systems they no longer try to keep a constant pressure differential across the injectors. They just measure the fuel rail and manifold pressure and let the ECU do the math to determine the necessary pulse width. 30 years ago the ECU's didn't have enough compute power to handle that so the pressure drop was kept constant by a pressure regulator mounted on the fuel rail that had a tap off the manifold for it's reference pressure. The pressure regulator bleed excess back to the tank in a return line. That very nicely accounted for the range of manifold pressures from decel vacuum to WOT turbo boost. Without a return line to the tank that doesn't work anymore. The injector static flow rate has a nearly perfect (delta P)^.5 relationship that's easily calculated and they can map in the change in injector response time as a function of pressure differential. Not sure exactly when they transitioned to returnless, I'm sure it took quite a few years, but I know my 2003 350Z was the first returnless system I've owned.

Also, with GDI systems the rail pressure is so high the cylinder pressure is insignificant. They ramp rail pressure up and down all over the place depending on engine speed and load.

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The motorcycle EFI systems that I'm familiar with, are returnless. The in-tank pump assembly contains a fixed-pressure regulator with no connection or accounting for intake manifold pressure. In the case of forced induction, the fixed regulated pressure is high enough to make sure there is always sufficient pressure across the injectors even at max boost pressure. The ECU simply does the required math.