Hi guys- nice forum you have here.

I have a very unique and unusual application for a turbocharger. After I read through some stuff here, it seems like this community would definitely be able to help, and I have a pretty good idea of what I'm doing (engineer by trade)...

I am designing a system that requires fairly low pressure air (15-30 PSI). Ultimately I am going to be raising the temperature of the air (to heat another process downstream), so I can use the natural inefficiency of compressing air to raise the temperature. Part of this process already uses an engine, but I don't intend on using the compressed air from the turbocharger to the engine (but use it somewhere else). Basically what I want to do is recover the otherwise "wasted" energy from the engines exhaust to drive this compressor.

The engine runs at a fixed speed (3600 RPM), and the engine is approx. 1.0L in displacement (twin cylinder, air cooled).

From an application stand-point, I don't see any reason why this wouldn't work fine.. The turbocharger's compressor doesn't care if the air goes into the engine or somewhere else.

What I want to do is size a compressor/turbine combo that will maximize the mass flow rate at this specific condition. In this application, it's somewhat beneficial to run the compressor in an inefficient part of the compressor map so that the temperature is raised more (what's most important is that mass flow is optimized, compressor efficiency is not so important so long as I'm inside the operating envelope). The higher the pressure the better, since higher pressure air will help with it's heat transfer properties.

What I'm not sure about is how to size a compressor/turbine combo so that I'm extracting the most amount of energy from the engine's exhaust. Obviously too small of a turbine will have too high of back pressure, and large of turbine and the engine may not be able to drive the compressor to it's desired operating range.

I appreciate any comments! #ad


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Will the engine be under any load? will be very hard to get a turbo the correct size for that. What about using a heat exchanger on the exhaust side In order to getting the charge temps higher?

 

Yes, the engine is going to be loaded (mechanically driving another load).

Assuming standard air density and VE, I'm seeing that engine should be able to push about 4.3 lb/min. I'm thinking I'd want to start with looking at the turbine map, and verifying that the mass flow across the turbine is going to be "on the map". For instance, looking at a garret T12 turbine map, 4.3 lb/min is barely on the operational line which means low back pressure but I'm concerned that it might be too close to the low end of operation.

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I was looking at the IHI RHB31 (VZ21). Here's some info on a cheap Chinese knock-off. http://www.ecotrons.com/products/small_engine_rhb31_vz21_turbocharger/ For some reason I can't find the compressor map, but I have it somewhere... In that documentation, they mention that it's suitable for up to 600cc engine (looks like it's used mostly on motorcycles), and my concern is that it's going to be too small.

 

I have used a Larger Compressor capacity on a smaller flow application by just adding a By-pass circuit that went thru a inter-cooler to cool the charge and then routed it back into the compressor inlet. As the mass flow requirement went up I just closed off more of the by-pass circuit. Worked very well for the size of the engine we were using. Maybe you could use the by-pass circuit (without the inter-cooler) for your task.

Tom Vaught

 

It sounds to me like he would rather capture all outgoing mass flow rather than divert any away from it's target though. He basically wants a charger that will flow the most CFM at his steady-state conditions, regardless of heat creation. This means mulling over the compressor maps and doing some calculations.

Garrett has some pretty good info that could help:
https://turbobygarrett.com/turbobygarrett/turbo_tech_expert

and

https://turbobygarrett.com/turbobygarrett/choosing_turbo

I didn't read through this but it may be of some help:
http://www.gnttype.org/techarea/turbo/turboflow.html

 

He needs to know how much air the engine is using now. Is it 3600rpm and WOT? I assume it's not. Does the throttle vary? I assume it does. Depending on throttle angle used to keep the fixed RPM, he may not find much that cam move that little air.

 

Is the volume of air or the temperature of air more of a concern? When you compress air, you compress the latent heat in the air as well. So building a shroud and ducting the heat coming off the air cooled engine into the turbo will multiply the heating effect of compression.

 

I would look into something related to go-kart engines. It'd be beneficial for you to state the intended use for the bewst.

 

I'm guess it's oil and gas and or power plant related guys. It sounds like he needs hot air at 30 ish pounds. What size is the piping post turbo? What size is the exit back to atmosphere?