2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello J.A.W.

You write:
“Well, that depends... on how far/fast you want to move.. if 1/2 speed/power is ok, then ~3 X distance..
See:
https://www.youtube.com/watch?v=ruTJ3A-7L5E”


According the above video:

1x250hp Evinrude E-TEC G2 250 H.O.
Peak power: 5700rpm, 115.3KPH, 83.7LPH, 211Km range.
Cruising: 3000rpm, 52.3KPH, 24.6LPH, 326Km range.

The overall resistance increases (more or less) with the speed square.

(115.3/52.3)^2=4.86, i.e. at the peak power / peak speed the resistance is almost five times higher than at the cruising.

In case the overall-BTE of the propulsion system (this includes the screw / propeller too) remains unchanged, the expected Fuel Consumption at the cruising is calculated at 83,7/4.86=17.3LPH (according the video, in practice it is 42% higher).
With 17.3LPH the range at cruising (52,3KPH) increases from the current 326Km to 463Km.

Reasonably the main cause of the poor overall efficiency at cruise is the screw: it is optimized for substantially higher than the cruise speed.

Interesting calculation: (3000/5700)*115.3=61KPH >>52.3KPH

A variable pitch propeller would decrease substantially the fuel consumption at cruising (without compromising in the maximum speed); well bellow 17.6LPH, because the engine operates at better conditions (lower rpm, lean mixture, more time for the preparation of the mixture and for the combustion of the fuel at higher expansion ratios etc).

We still can’t say what is the efficiency of the Evinrude E-ETEC at partial loads (by the way, in the new Hirth site I cannot find Fuel Consumption data).
The BSFC graphs for the Evinrude E-TEC, Rotax E-TEC and Mercury Optimax would be quite useful.


You also write:
“Obviously, a heavy marine diesel of the same power rating - would def' not suit that boat.. or go as fast..”

“would def' not suit that boat”: Maybe yes.
“… or go as fast”: Definitely no.

Here is a “heavy” marine Diesel alternative arrangement (Volvo IPS (Inborad Performance System)):








For the same range it requires way less fuel (that compensates, at least partly, its heavier weight and, in the long term, its higher cost).

Spot on the double counter-rotating “pulling” propellers and on the clever mounting of the propulsion system..


Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis, indeed for efficiency, the variable pitch/contra-rotation prop is worthwhile, even for
a 'personal' flyer.. & it is odd that Hirth does not offer a metric equivalent to the figures in the U.S. format.
Perhaps, if it is of sufficient curiosity value , send an email to their tech address to ask for it?

Anyhow, this site: http://www.boat-fuel-economy.com/evinru ... us-gallons
Which you linked/cited earlier - may provide some of the E-TEC part throttle data - of interest.

For a 'buoyancy' vehicle such as a boat or aircraft, there are manifold parameters of weight/drag distribution
to add up.. ..could the heavy diesel engine lift the same hull out of the water onto plane at efficient cruise speed?

Here is a comparison of large outboards of 300+ hp, ( inc' 4Ts) note the period of plane lift/over 3mpg consumption cruise: http://continuouswave.com/whaler/refere ... 510Bay.png

The latest hi-po Evinrude is to feature a variable exhaust port timing valve, such as the Ski-Doo uses..

[Pierce89]

Hi Manolis, indeed for efficiency, the variable pitch/contra-rotation prop is worthwhile, even for
a 'personal' flyer.. & it is odd that Hirth does not offer a metric equivalent to the figures in the U.S. format.
Perhaps, if it is of sufficient curiosity value , send an email to their tech address to ask for it?

Anyhow, this site: http://www.boat-fuel-economy.com/evinru ... us-gallons
Which you linked/cited earlier - may provide some of the E-TEC part throttle data - of interest.

For a 'buoyancy' vehicle such as a boat or aircraft, there are manifold parameters of weight/drag distribution
to add up.. ..could the heavy diesel engine lift the same hull out of the water onto plane at efficient cruise speed?

Here is a comparison of large outboards of 300+ hp, ( inc' 4Ts) note the period of plane lift/over 3mpg consumption cruise: http://continuouswave.com/whaler/refere ... 510Bay.png

The latest hi-po Evinrude is to feature a variable exhaust port timing valve, such as the Ski-Doo uses..

Variable exhaust port timing valve...lol
Motocross 2 strokes call that a powervalve and its been around since the 80's

[J.A.W.]

Not only race machines such as MX bikes, road bikes had them from back then too, followed by other sporting 2Ts.

I have a mid 80's Yamaha RZ 350 road bike, & as a matter of interest those "Power Valves" are in fact, 'economy valves' too.

[manolis]

Hello J.A.W.

You write:
“Perhaps, if it is of sufficient curiosity value , send an email to their tech address to ask for it?”

Not only Hirth but all the 2-stroke engine makers should give the BSFC tables of their engines.
Unless they have something to hide.


You also write:
“Anyhow, this site: http://www.boat-fuel-economy.com/evinru ... us-gallons
Which you linked/cited earlier - may provide some of the E-TEC part throttle data - of interest.”

They give the fuel consumption at various rpm.
However, without knowing the power at these revs the Break Thermal Efficiency cannot be calculated.
Only the peak power is given, and there is where the BTE is calculated.


You also write:
“For a 'buoyancy' vehicle such as a boat or aircraft, there are manifold parameters of weight/drag distribution
to add up.. ..could the heavy diesel engine lift the same hull out of the water onto plane at efficient cruise speed?”

You are right; unless the weight of the additional fuel required by the lightweight, but inefficient, engine “counterbalances” the increased weight of the efficient engine

In the Flyers the BTE gets even more crusial.
In an older discussion the BTE of the small turbines used by Yves Rossy was calculated at 2%.



Some 30Kg of fuel is consumed in 10 minutes.
With a lightweight 2-stroke engine having 20% BTE, the same fuel lasts 100minutes.
With a lightweight 2-stroke engine having 30% BTE, the same fuel lasts 2.5 hours.

Lightweight like, say, the PatTwo:



the UK patent for which is scheduled to be granted next month.

Or, say, lightweight like the double (for safety) OPRE Tilting propulsion unit:




The ideal would be to combine the lightweight / simplicity of the two-stroke with the fuel efficiency of the 4-stroke Diesels.

A Cross Radial PatAT two-stroke turbocharged Diesel:



is capable to combine a higher BTE than the VolvoPenda four-stroke Diesels with a lower weight than the lightweight Evinrude / Rotax / Mercury high-tech two-stroke engines.

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis,
- here are a couple of power graphs which show the typical 2T torque advantage, such as shows up in 'getting on the plane'.
http://www.evinrude-outboards.co.uk/decor/charts.gif




Best wishes for your endeavours, powered flight-wise.

[manolis]

Hello J.A.W. and thanks for the wishes.


Regarding the “Two-Stroke Torque Advantage”, the two engines in the graph:



have the same capacity (3.4L) and the same (?) peak power (225HP).

Using the data provided by the above graph the following Power – Torque graph was made:



(white / red : Evinrude torque / power)
(cyan / blue: Yamaha torque / Power)


A few interesting things:

The one engine has some 10% higher power output (250HP vs 225HP). So they are not really comparable.
It seems like they used in the test a 250HP Evinrude E-TEC instead of a 225HP Evinrude E-TEC. If so, this "halves" the torque advantage of this 2-stroke.
See how the torque of the one is always higher than the torque of the other along the complete rev range (the two torque curves never intersect).

The two-stroke has, as expected, a higher peak torque than the same capacity four-stroke. But the torque of the two-stroke drops steeply after 4,500rpm (so steeply that the power is not increasing after 4,500rpm; as in the direct injection Diesels; maybe the E-TEC Direct Injection requires more time for the preparation of the fuel as in the Diesels; or maybe the breathing / scavenging is too inefficient at higher revs).
On the other hand, a conventional 2-stroke can make way more torque (such as 50% or 75% more) than an equal capacity four-stroke.


Maybe the Evinrude E-TEC is oriented to lower fuel consumption.

However, with the data provided at http://www.boat-fuel-economy.com/evinru ... us-gallons, the BTE of the Evinrude E-TEC 225HP 2-stroke at peak power is 21% lower than the BTE of the Yamaha 225HP 4-stroke (21.5GPH versus 17.7GPH).
Calculated BTE of the Evinrude ETEC 225 at peak power: 22%
Calculated BTE of the Yamaha 225 at peak power: 27%


With similar capacity, similar weight and similar power (Evinrude 225 2-stroke / Yamaha 225 4-stroke), what is the real advantage of the two-stroke over the four-stroke?

The price?
However the four-stroke appears cheaper.

The middle range BSFC of the E-TEC?
As I wrote again, the two-stroke engine makers should provide the BSFC graphs of their engines to persuade their potential customers that their engines are as good as the 4-strokes (or better).

The two-stroke engine makers should provide true data, not like those for the Hirth 3703.

Now they use advertising tricks like: "30% lower fuel consumption than our previous model".
Who cares about your previous model?
Just give the real fuel consumption; and then accuse, as much as you like, your previous model for inefficiency.

Am I wrong?
Did you find, so far, an official BSFC for the Rotax E-TEC / Evinrude E-TEC / Mercury Optimax high-tech two stroke engines?

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis, a couple of points, buyers looking to replace an engine would find an efficiency improvement of interest,
& indeed the 250 hp engine - is more powerful yet.

The torque produced is what enables the boat to surge up out of hull displacement motoring onto 'the plane'..
Honda have added complexity via the 'VTEC' system to emulate this, & Mercury like-wise with supercharging.
These 4Ts require many more costly parts & servicing schedules - to achieve anywhere near the 2T's output,
reflecting the more highly stressed, harder tuned engine - which a competitive 4T needs.

The decision to incorporate an exhaust 'power-valve' in the hi-po E-TEC engine variant is likely a recognition
of this power broadening feature, one long since used in smaller capacity engines.

Brian Coat, a few pages back, posted this research paper: http://publications.lib.chalmers.se/rec ... 149154.pdf

It features a laboratory test of the Evinrude E-TEC including BSFC.

Hirth may well thank you, if you point out the perceived errors in their published documentation,
I doubt it is a deliberate misrepresentation, especially in the USA, where lawsuits fly like confetti.

[manolis]

Hello J.A.W.

You write:
“buyers looking to replace an engine would find an efficiency improvement of interest, & indeed the 250 hp engine - is more powerful yet.”

The graph showing the Torque Advantage of the two-stroke versus the four-stroke is misleading.
The average “customer” is not able to see the “innocent” mistake (i.e. that the Evinrude is the 250HP, while the Yamaha is the 225HP).



You also write:
“The torque produced is what enables the boat to surge up out of hull displacement motoring onto 'the plane'..
Honda have added complexity via the 'VTEC' system to emulate this, & Mercury like-wise with supercharging.
These 4Ts require many more costly parts & servicing schedules - to achieve anywhere near the 2T's output,
reflecting the more highly stressed, harder tuned engine - which a competitive 4T needs.”

The increased torque of a two-stroke is one of its main advantages: it allows a substantially smaller engine capacity and engine weight.
In the specific comparison (Evinrude 225 vs Yamaha 225), the two engines have the same capacity and the same weight. The increase of the torque (case wherein the two-stroke is the 225HP and not the 250HP) is not as big as it should.

The lower cost is another main advantage of the two-stroke.
However in practice, the four-stroke Yamaha F225 (with the “many more costly parts”) appears cheaper to buy than the two-stroke Evinrude E-TEC. It also appears cheaper to run (fuel cost).

The two-strokes do have strong advantages over the four-strokes.
But they have also significant disadvantages / issues to be addressed.



You also write:
“Brian Coat, a few pages back, posted this research paper: http://publications.lib.chalmers.se/rec ... 149154.pdf”

Thanks.
Here is the BSFC graph (lab measurements from a master thesis).



A few interesting things:

The Evinrude E-TEC 25HP at 4,000rpm is at its best: it runs at a BTE from 26% to 29%.

At peak power the BTE is 23%.

After 4,000rpm the power is not increasing.

The value 264.5gr/kWh at (2,500rpm – 1.5bar) seems wrong (compare to neighbor values).


What we need now is the BSFC graph of a similar power four-stroke outboard engine.


Thanks
Manolis Pattakos

[J.A.W.]

No Manolis, both engines were 225 hp models.. & as I noted, the 250 hp E-TEC has more power yet.

As for weight, you have to take into account that the basic 2T engine is lighter, & more compact,
- but the measured weight includes the engine mounting & integral powered tilt/trim systems on the Evinrude.

Here is a dyno chart comparison of a simple piston port 2T, ( this is the machine described in the final post on page 79) with its 4T competition of 40+ years ago, note the torque output of the two 750 triples shown:

http://www.kawtriple.com/mraxl/articles ... bikes2.htm

& here is a pair of higher specific output Yamaha 350 2Ts from ~15 years later, using reed valves for inlet timing control,
& exhaust 'power valves' to boot, & note the newer one of the pair- has received a power increase tune too.




If you re-check the second link in my first post on this page, you will see that in fact - the current high output E-TEC marine engines offer a significantly better fuel consumption profile, than their 4T rivals, with more improvement to come..

The provision of such dynamic control for the new E-TEC outboard allows a for a like power range improvement, as shown by the 2T Yamaha sports motorcycle engines.

[J.A.W.]

Hi Manolis, this thread linked below shows the BSFC data for the 250 hp class DI 2T engines at various power settings.

http://www.continuouswave.com/forum/vie ... ?f=7&t=125

[gruntguru]

Nice find there Jaw.
268 g/kW.hr is not a bad number but it is unlikely to be the peak efficiency of that motor since it occurs at ICOMIA mode 2 which is at 40% of rated speed (peak-power-speed) and 25% of peak-power-torque. Best efficiency usually occurs near peak torque speed and about 70-80% load. For the E-TEC 250 those numbers (assuming peaks 275 hp @ 5,000 rpm and 345 lb.ft @ 3,500 rpm) are approximately:

ICOMIA 2 OPERATING POINT
73 lb.ft @ 2000

TYPICAL BEST EFFICIENCY OPERATING POINT
260 lb.ft @ 3,500

Of course the latter could be wildly inaccurate since it assumes similar conditions for peak BSFC as apply for four stroke engines.

[manolis]

Hello J.A.W.

You write:
“No Manolis, both engines were 225 hp models.. & as I noted, the 250 hp E-TEC has more power yet.”

OK.

I checked it with the data provided at http://publications.lib.chalmers.se/rec ... 149154.pdf for the Evinrude E-TEC 25HP and it happens the same:



The 25HP Evinrude ETEC actually makes 31HP peak power.

Worth to mention: the peak power is provided at 4,200 rpm and not at 5,800rpm (i.e. not according the specifications).


An engine maker offers an outboard engine as making 225HP (or as making 25HP) output power, but the engine actually makes 250HP (and 31HP respectively).

31HP is 24% more than 25PH.

The engine maker could simply say that for similar capacity their two-stroke has a 27% torque advantage over the four-strokes.


You also write:
“this thread linked below shows the BSFC data for the 250 hp class DI 2T engines at various power settings. http://www.continuouswave.com/forum/vie ... ?f=7&t=125 “


Quote from the above link:

“During the dealer meeting in 2014 when Evinrude revealed their new E-TEC V6 74-degree engine, a slide was presented that showed the brake specific fuel consumption of the new engine at various loads. The slide looked like this:




In this bar graph presentation, a lower bar is the better value, as the data is for rate of fuel consumption, and lower fuel consumption is better. (Note that the legends "High Speed" and "Low Speed" are reversed in this slide from the actual speeds.)

. . .



End of quote


A conventional BSFC graph would be more useful.
As it is now, it is not clear what the various modes (from High Speed to Low Speed) stand for.

On the other hand, at medium-high speed the Evinrude E-TEC operates at 30% Break Thermal Efficiency (268gr/kWh), and at high speed it operates at 28.5%BTE.
At its worst mode (low speed) the E-TEC runs at 24%BTE.

At its best mode (high speed) the Yamaha operates at 27% BTE. At its worst mode (low speed) the Yamaha operates at 20% BTE.

At its best mode the Mercury Optimax operates at 26% BTE, at its worst mode it runs at 22.5% BTE.


The by far winner is the E-TEC two-stroke:



See the shape of the combustion chamber, the location of the spark plug / fuel injector and the squeeze area and compare with:



I wonder how the PatRoVa four-stroke would behave with the E-TEC direct injection of the Evinrude / Rotax.

Thanks
Manolis Pattakos

[FW17]

What is the type of lubrication on the Evinrude E-TEC?

[J.A.W.]

Nice find there Jaw.
268 g/kW.hr is not a bad number but it is unlikely to be the peak efficiency of that motor since it occurs at ICOMIA mode 2 which is at 40% of rated speed (peak-power-speed) and 25% of peak-power-torque. Best efficiency usually occurs near peak torque speed and about 70-80% load. For the E-TEC 250 those numbers (assuming peaks 275 hp @ 5,000 rpm and 345 lb.ft @ 3,500 rpm) are approximately:

ICOMIA 2
73 lb.ft @ 2000

BEST EFFICIENCY
260 lb.ft @ 3,500

Of course the latter could be wildly inaccurate since it assumes similar conditions for peak BSFC as apply for four stroke engines.

Or, could it be that such an efficiency point - is an artifact of the transition from stratified charge to full SI running?