Can You Turbocharge a 62 cc Two-Stroke Engine?

[fredric21]

Ok, here's the maths. Total mass flow through engine is 18,750 litres/min. for bmep 460 psia at n=12
Piston area = 25.136 Stroke = 0.1ft. rpm = 12,500
Using formula BHP = PLAN/33,000 = 431
At 17,550rpm, BHP= 605 for piston speed of 58ft/sec.

 

[bluechipx]

Ok, here's the maths. Total mass flow through engine is 18,750 litres/min. for bmep 460 psia at n=12
Piston area = 25.136 Stroke = 0.1ft. rpm = 12,500
Using formula BHP = PLAN/33,000 = 431
At 17,550rpm, BHP= 605 for piston speed of 58ft/sec.

It sounds like you are getting your 605hp from 500cc, 'in theory'. If this is not the case, please give the details about the engine you are talking about.

 

[fredric21]

Yes, of course this is pure theory...what else!
However, the prototype is under construction and I will let you know the real world results in due course, when I get it on the test bed.

 

[bluechipx]

As far as I know, top fuel would have to be on top of the HP/cubic inch battle. At 500 CI and approx 8000 HP they have achieved 16 HP per cubic inch with supercharged nitromethane. The price is a motor that must be dis-assembled and rebuilt after several seconds. Does anyone know about any motor from R/C on up that has a higher HP/CI?

 

[fredric21]

My old-time colleague, Peter Halman who now is a partner with Ripmax Ltd, has produced a 2.5cc, 0.15cu.in. glow motor that actually produces 2.5BHP at 40,000 rpm on methanol only...no nitromethane or other oxygen-bearing additive.
I believe the bore to be about 14mm, giving a piston area of 0.239 in2., or 10.46 BHP/in2. of piston area and 16.67 BHP/cu.in.
I have run one of these engines for 30 minutes at full bore, with no deteriation of parts.

 

[fredric21]

Excuse me, but a supercharger for scavenging and a turbo for boosting the charge pressure is the only way to go in two-stroke development. Get rid of piston-controlled porting and you have a winner.
460 psia BMEP's are easily possible with such a set up. Check out the Rolls Royce Crecy from 1944.

 

[bluechipx]

The Rolls Royce Crecy from 1944 is a four stroke used for aircraft. It is 3,200 BHP and about as far from a two stroke as would be possible.

 

[fredric21]

I must correct you here. The RR Crecy was most definitely a two-stroke and had Ricardo-type sleeve valves.
If you don't believe me, I suggest you read the book on the Crecy by Nahum, Foster-Pegg and Birch, which is the definitive work on this engine.
On a further note, the prototype of my sleeve-valve two-stroke engine design is now nearing completion and I anticipate the first test runs within only a few weeks ...very exciting!

 

[bluechipx]

I'll concede you may be right about the 1944 monster engine not being a four stroke. Up until your post I never heard of it anyway and a wiki check made it look about as far as possible from anything that would be of use to me. Keep us posted on your project with pics if possible.

 

[fredric21]

What on Earth are you talking about when you say that superchargers are "overkill" for two-stroke engines?
If, as you suggest, we are to keep the two-stroke engine "simple", by which I assume you mean piston-ported and crankcase scavenged, then you are stuck with resonating pressure pulses to effect the scavenging processes. POPPYCOCK I say.
Only a sophisticated re-design of the entire two-stroke cycle of events will do if, we are to compete with the four-stroke in terms of fuel consumption, noise, longevity, and atmospheric pollution.
Piston porting is out entirely as is crankcase scavenging. Poppet valves are hopeless in a high-speed two-stroke, so sleeve-valves hold the only hope.
Effective scavenging by means of a supercharger carefully mapped to peak mass airflow and a turbocharger to raise both the exhaust pressure and the induction pressure using the residual energy contained in the exhaust mass flow will raise BMEP's from around 80psia to around 460psia.
Now tell me superchargers are "overkill".

 

[bluechipx]

A large percentage of drag race two stroke snowmobiles are turbocharging and the number is growing fast due to the easily gotten high horsepower available with a turbo system. I get around a lot and have never seen a supercharged two stroke work yet, other than in conversation with a bunch of so called inventors, so I remain sceptical. The turbo only on a two stroke is popular because it actually works.

 

[fredric21]

Hi bluechipx,
This was meant to be a reply to chkneater posted on Jan 10th. this year.
But, as we are on the subject, check out the Chrysler Two-stroke engine developed for the Neon. See:http://www.allpar.com/neon/stroke.html
Are you still sceptical?

 

[fredric21]

Hi Bluechpx.
I thought I would keep you up to date on progress with my own radical two-stroke design.

At long last I have completed the prototype and it is installed on the test bed.
I have had some problems with oil supply which have now been sorted, but I still need to sort out the ignition system.
I have to supply over 1000 high intensity sparks per second through just one spark plug!

Of course, I am using a supercharger(with intercooling)...as well as an exhaust turbo.

(The resistance to exhaust flow increases the scavenge pressure of the Supercharger and this increases the induction boost pressure into the cylinder.)

Ricardo found that this measure increased cylinder filling to 2.89 times that of "normal" four-stroke filling, and this in a two-stroke!

I have already motored the engine up to 20,000 rpm with no mechanical problems. I will keep you posted with developments.

 

[DannoXYZ]

fredric21 & bluechipx,

Please keep posting on your progress. I've been following this thread and your information is most fascinating!

 

[flogge]

A turbocharger compresses at the intake side and restricts at the exhaust side. It effectively makes the engine think it's running in a higher atmospheric pressure. If a turbocharger raises the pressure on the exhaust and intake equally, the volumetric flow rate is equivalent at a given engine RPM. If this is true then the differential pressures at the ports remain the same and so the flow characteristics of the engine are unchanged. The mass flow rate is improved because of a denser charge. In actual practice, any turbocharger has different efficiency levels at different flow rates.

 

[HowlerMonkey]

Napier Nomad had a "specific fuel consumption" of 0.36 lb/(hp·h) (0.22 kg/(kW·h).

Turbocharged and supercharged two stroke.

 

[OldEngr63]

The big boys like Detroit Diesel and EMD have been running turbochargers for many years, so why would anybody say that turbocharging is out of the question for 2-stroke engines? What is fundamentally different in the smaller engines?

 

[Fairadvantage]

Just stumbled on your site and offer a cool turbo project I built in 2010 and tested in 2011. This will put to bed questions about the feasibility of two stroke turbos. At 56.1 CI, this may be the smallest successful 2-stroke turbo outboard ever built. Volumetric formulas predict it delivers 153 HP at 8000 RPM. Am pretty sure it's all of that. Seach youtube for Tim's turbo Johnson and you can see/hear it run. Fantastic!

Tim