Why.
As a opening comment the developer of the FlyGas supercharger has seen NO need for inter-cooling at the time of writing and historically no problems have been reported.
Australia can see extreme temperatures of 45 C plus so runway temperature off 60 C can be possible as a worst case possibility. Reference to my book on auto superchargers show's a boost of 6 psi should not take an engine with suitable fuel too detonation but at 60 C it would be getting tighter.
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| Effect of inlet temperature on outlet temperature Ford Mustang 5 litre |
The chart is based on a 71 F which is about 21 C so at a theoretical 60 C inlet temperature could reach 95 C for a short period and this is the problem Jack Riley encountered with his turbo normalized Lycoming upgrades of the 1960s.
[The writers opinion is that short period, light detention was the reason it appeared after time in service]
Extract Rotax 914 owner manual Section 4
"This sensor monitors the air-box temperatures. The TCU operating program is designed to reduce boost pressure if this sensor indicates the air-box temperature is above 72ºC (162ºF). In the normal course of running a turbo, the natural compression of air (adiabatic compression) as well as heat transfer from the hot turbo, raises the temperature of the incoming intake air. Testing has shown that intake air temperatures below 60ºC (140ºF) provides an adequate safety margin in preventing detonation in the engine in the event of a lower octane fuel and a high intake air temperature. In cases where the air-box temperature is run between 60ºC (140ºF) and 72ºC (162ºF), a higher octane fuel must be used "
Refer: Tornado Alley Turbo on this subject
"A current technology good inter cooler design can reduce the induction air temperature so that turbocharged or turbo-normalized engines see induction air temperatures that are much more comparable at all altitudes and power settings to a hot day normally aspirated engine than they are to a non-inter cooled turbocharged engine"
So put simply I have a developed prejudiced for the use of a inter-cooler not as a power boost but as added insurance - cost about 2.9 kg.
Design
After reference to my automotive design reference on inter-cooling a Bell Intercoolers aluminium 14 x 5 x 2.5 inch ordered but at the time weight was not considered and its a little heavy at 2.15kg.
The design of the structure is a major issue as there are no 3D models so all the design is based on 2D drawings and site measurements. After a lot of thought it was decided to collect the boosted air in the front tank, pass it through the core to a rear tank and finally to the carburettors to create space and flexibility for connection to the engine.
The struts are there as I cannot see a way to connect it to the engine mount but it may most likely end up there in the real world. The current weight as shown is 3.24 kg but involves a lot of turning to remove all unwanted weight and doing it again a 2'' core would be more than adequate and save about 400 grams.
All connections will be done using 2'' OD SCEET hose allowing the blending between the various outlets. It is lighter that silicon, flexible and has a suitable pressure rating. As part of the manufacture a JEGS beading tool will be used to bead all connections and all connections will be double clamped. The completed unit will be load tested to 7g at assembly to verify the design.
A final check will be done on my return and if confident all the components will be machined and assembled at a local engineering shop. The last item to be installed is the inlet pipe as I suspect that it may have to be relocated but that will require installation of the engine and supercharger.
The final baffle and inlet design is up in the air but one step at a time.
Is it worth while - well if it works I will never know but its insurance.
Draft Design
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| View from underside |
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| View from top side |
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| Plan View Tank 80 mm OD @ 164 mm centres - outlet 462 mm centres Tank overall 373 mm Cut-out at rear is to clear hydraulic cylinder mount may be relocated to under side |
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