Alternative fuel enrichment

[Tom68]

Some engines like power adders or two strokes are partly fuel cooled.
They cannot take leaning out to best power AFR without overheating.
Maybe they could with less ignition lead?
21% of the air is oxygen and that burns with the fuel.
The nitrogen expands when heated together with the parts taking part in combustion.
Highest charge heat gives most expansion and most pressure.
So it is when going towards maximum pressure you can burn stuff, richer or leaner runs cooler.
There can be some surfaces like 2 stroke pistons that need the extra fuel cooling though.

Erland

In the 2t example, I've never been able to find actual AFRs for them. But yer, when they lean to destruction they are probably still way richer than stoich, so rich on a stoich scale and even richer than max power when they heat the piston enough to seize it.

Of course a 2t gets no rest, not only does it have to fire every time the pistons up top but the crankcase is a non intercooled blower so the piston is already hot from compressing the next charge.

Of course the other thing with taking fuel out of a 2t running on premix, you're taking lube out as well.

[David Redszus]

While we can predict how much fuel is required for any blend, we do not know
how the fuel will evporate, its evaporative cooling, its ignitability, combustion properties,
power production, completeness of burn, flame temperature, carbon deposits, etc.

So David, when choosing an optimum fuel for a given engine and it’s intended purpose the octane rating must be a primary consideration.

Octane is a parameter that must be considered. But the operating conditions have a significant effect on octane performance, as does fuel ratio and preparation.

If there are multiple fuels to choose from that will have a suitable octane rating but have different specific gravity is a higher or lower specific gravity preferable or, is it inconsequential?

Specific gravity has no direct effect on octane performance. As we have discussed, SpG should be used to determine enrichment. For a given enrichment, a fuel with a higher SpG will provide better fuel economy which could be important for endurance racing.

I dare say by your last paragraph above there is more to it and an interrelationship with other aspects like the rvp and h/c ratio?

There is quite a bit more regarding fuel properties and improved performance.

Which topical areas would be of interest regarding fuels?
We could start new threads for specific fuel topics if there is any interest.

[HQM383]

Which topical areas would be of interest regarding fuels?
We could start new threads for specific fuel topics if there is any interest.

Many topical areas of interest.

First up, what property of fuel for high performance engines do we give too much consideration and what property not enough consideration when selecting a fuel blend?

Too low an octane rating effects is well known but what are the indicators of using too high an octane rating?

Likewise, what are the signs of too high and too low of an RVP value?

[RDY4WAR]

Too much consideration: Octane (it's the ONLY thing considered by a lot of people)

Too little consideration: Distillation / RVP

[HQM383]

Too much consideration: Octane (it's the ONLY thing considered by a lot of people)

Too little consideration: Distillation / RVP

Octane is probably akin to cylinder head cc’s regarding consideration.

Distillation/RVP; elaborate why this factor should be given more consideration.

[David Redszus]

Overconsidered: Octane

The sole purpose of octane is to avoid detonation destruction of the engine, while permitting
the use of higher compression ratios.

Effective octane can be altered by use of ignition timing, inlet air temperature, combustion
charge motion (squish), fuel ratio, head temperature, and mixture preparation.

One area of octane confusion results from the octane terminology being used; RON, MON, Index,
rich, Road.

Research Octane Number (RON) should not be used for performance engines. It overstates.

Motor Octane Number (MON) is the only octane number to be used for performance engines.

Index (RON + MON/2) is the average of RON and MON and is the number found on gas pumps.
It has limited value since it is skewed by the inflated RON value.

Rich Octane is used by the aviation industry and refers to octane value increased by use
of excessively rich mixture during takeoffs. The rich mixture is quickly returned to normal
after takeoff.

Road Octane is the actual octane experienced by the engine while on the road during actual
operating conditions. It is a function of mixture ratio, preparation, temperature, rpm, load
and timing. It is best determined by use of knock sensors.

Depending on the above road conditions, we need enough octane to prevent engine
destruction and to allow adequate engine power. But more octane than necessary
does not improve performance. Neither does it detract from performance.

Octane values have NO effect on flame speed, burn angle, ignitability, or completeness of burn.
Suppose we fuel and baseline an engine on the dyno with an unleaded 100 MON fuel.
Now we add 4 gr TEL to the unleaded fuel to raise the octane to 120 MON. No change in engine
performance can be observed. But higher octane would allow more aggressive tuning.

However, it is possible to compare fuels of identical octane values and see a difference in
observed performance. This is not due to the difference in octanes but to the composition
of the fuel. A racing gasoline may contain over 50 compounds in variable amounts, each with a
different performnce characteristic. I have examined pump gas that contained 484
components; the following week the same blend source contained 524 components.

Lead, in the form of TEL or TML is often used to increase octane. The ability of lead
compounds to raise octane depends on the basestock to which it is added. Lead will
actually lower the octane value of some fuel components. Use caution when blending
leaded and unleaded fuels to improve octane.

[HQM383]

Effective octane can be altered by use of ignition timing, inlet air temperature, combustion
charge motion (squish), fuel ratio, head temperature, and mixture preparation.

Ignition timing, fuel ratio and to a degree mixture preparation are post engine build tuning variables, the others not so much. So should our fuel be chosen first to build around rather than the other way around and build an engine and then find a fuel to suit?

Octane values have NO effect on flame speed, burn angle, ignitability, or completeness of burn.....

Without going into great detail yet, what dictates flame speed, burn angle, ignitability and completeness of burn?
Maybe start with ignitability.

[HQM383]

Anyone have input into what can be a very enlightening thread?

Engines don't run without fuel so it would be great to learn more about the quiet achiever of power production.

[Tom68]

Anyone have input into what can be a very enlightening thread?

Engines don't run without fuel so it would be great to learn more about the quiet achiever of power production.

Interesting point in the Mark Campbell live chat, he mentions quench being dropped by some for emissions, accessible chamber burns all the fuel, quench chamber leaves unburnt fuel, makes more power and suppresses detonation.

[juuhanaa]

Some engines like power adders or two strokes are partly fuel cooled.
They cannot take leaning out to best power AFR without overheating.
Maybe they could with less ignition lead?
21% of the air is oxygen and that burns with the fuel.
The nitrogen expands when heated together with the parts taking part in combustion.
Highest charge heat gives most expansion and most pressure.
So it is when going towards maximum pressure you can burn stuff, richer or leaner runs cooler.
There can be some surfaces like 2 stroke pistons that need the extra fuel cooling though.

Erland

Hii,

Would it make sense to try monkeying with the 2 stroke flat top pistons and make a dish there, to reduce the piston heat when the engine reacts to the ignition advance big time like rotax etec? If so would the fuel enrichment then be less, needed?



-juhana

[juuhanaa]

Hopefully thaat wasnt too much off topic.. I also did revisit Mark Campbell's live chats this weekend. He mentioned pistons, which i cant remember now, but which were the best thing since sliced bread. He also talks 8 to 1 motors, 8 to 1, 8 to 1!!!

I just wanted to add what i learn from my go drivers snowcross sled in 2019 or so. We both like to use power up products, but not in our morning porridge even some may say.. In any case, usually these 2-stroke engines use 3-4 percent oil in the fuel, regardless of the sled. Harri used 1.5% all season in Arctic-Cat and the parts looked cleaner and didnt wear as much! Some say that that reduced compression, but at the end of the day isnt it the pressure after TDC that counts?



-juhana

[David Redszus]

Two stroke engine specs:
B-54.0
S-54.5
R-110
cc-9.0
SCR- 14.87
EO- BTC -84,= 8.07 DCR
EO -BTC -82,= 7.82 DCR
EO-BTC - 80,= 7.58 DCR
EO-BTC - 78, =7.33 DCR
Compression ratio depends on exhaust port timing.

Depending upon the type of racing and type of oil, 4% is very light; suitable for trail riding.
Race engines normally run 7% oil of a modern type oil.

[juuhanaa]

Thanks for info. I just thought less oil and cleaner parts might indicate a cleaner charge and higher cylinder pressure.

This years Snow Cross sled has some Renault decals on it, but that doesnt mean ive touched the engine

Screenshot_2023-02-26-12-43-11-12_92460851df6f172a4592fca41cc2d2e6.jpg

-juhana

[jacksoni]

Two stroke engine specs:
B-54.0
S-54.5
R-110
cc-9.0
SCR- 14.87
EO- BTC -84,= 8.07 DCR
EO -BTC -82,= 7.82 DCR
EO-BTC - 80,= 7.58 DCR
EO-BTC - 78, =7.33 DCR
Compression ratio depends on exhaust port timing.

Depending upon the type of racing and type of oil, 4% is very light; suitable for trail riding.
Race engines normally run 7% oil of a modern type oil.

In more common usage, 7% is close to 15:1 oil mix? Is this right? I have seen some people suggesting ratios in this level with adjustments in mixture to make up for the extra oil My engine builder suggests 28:1 and I have been running 24:1 and so far without piston issues. Due to data logger problems don't have EGT's and as has been mentioned recording AFR by O2 sensors is hard. I am leaning on it though, 90seconds WFO but with no greater than 120* water temp (usually much less) and about 50* IAT. I'd like to lean it some for best power.

[David Redszus]

Two stroke engine specs:
B-54.0
S-54.5
R-110
cc-9.0
SCR- 14.87
EO- BTC -84,= 8.07 DCR
EO -BTC -82,= 7.82 DCR
EO-BTC - 80,= 7.58 DCR
EO-BTC - 78, =7.33 DCR
Compression ratio depends on exhaust port timing.

Depending upon the type of racing and type of oil, 4% is very light; suitable for trail riding.
Race engines normally run 7% oil of a modern type oil.

In more common usage, 7% is close to 15:1 oil mix? Is this right? I have seen some people suggesting ratios in this level with adjustments in mixture to make up for the extra oil My engine builder suggests 28:1 and I have been running 24:1 and so far without piston issues. Due to data logger problems don't have EGT's and as has been mentioned recording AFR by O2 sensors is hard. I am leaning on it though, 90seconds WFO but with no greater than 120* water temp (usually much less) and about 50* IAT. I'd like to lean it some for best power.

The actual oil ratio will depend upon the type of oil used. Some two-stroke oils are designed for use
with oil injection engines, and will contain a diluent to allow cold weather oil flow. When determining
oil ratio, the diluent must be considered.

Two stroke engines are not simply tuned for best combustion. Fuel ratio, oil, and ignition timing are often adjusted in order to obtain a specific EGT to optimize exhaust pipe tuning. The objective is to find the
best combination of combustion and pipe tuning.

Even with two-stroke engines, Lambda is far more important than EGTs; the best is to use both, one for engine, one for pipe tuning.