New Owner Advice... petrol and updates

[Thackeray]

Many thanks for all the explanations. I think I'm a bit clearer on what is going on here.

I was going to say that it's a bit misleading of Lexus to say that the IS300h has a compression ratio of 13:1. From the explanations here, it sounded as if they should be saying the expansion ratio (not the compression ratio) is 13:1.

And then I came across this site which has some graphics of the issues. Effectively, they seem to be saying the same thing as I was thinking - namely that Lexus should call this the expansion ratio. But then on the other hand, do Lexus technical departments really not know the difference between the compression ratio and the expansion ratio? It's all a bit puzzling.

[ColinBarber]

4 hours ago, Thackeray said:

Many thanks for all the explanations. I think I'm a bit clearer on what is going on here.

I was going to say that it's a bit misleading of Lexus to say that the IS300h has a compression ratio of 13:1. From the explanations here, it sounded as if they should be saying the expansion ratio (not the compression ratio) is 13:1.

And then I came across this site which has some graphics of the issues. Effectively, they seem to be saying the same thing as I was thinking - namely that Lexus should call this the expansion ratio. But then on the other hand, do Lexus technical departments really not know the difference between the compression ratio and the expansion ratio? It's all a bit puzzling.

I'm not sure they could state the expansion ratio because 99% of people wouldn't know what an expansion ratio is or why it is different from the effective compression ratio.

Why such a concern? Does it really matter? Technically the engine does have a compression ratio of 13:1 and at the end of the day running the Atkinson cycle improves efficiency by around 10% and the negatives associated are compensated by using a CVT transmission and additional power, when required, by the electric motors.

[reeac]

The essential point of the Atkinson cycle, as invented by Mr Atkinson over 100 years ago was to have a longer working stroke in order to extract more work from the combusting  fuel mixture. He achieved this with a very weird linkage between con rod and crankshaft (Google to find an animation). Toyota achieved the same end by crafty valve timing so that the effective compression stroke was shorter than the actual working stroke. The geometrical c.r. is 13:1 but the actual c.r is nearer 10:1. What I don't understand is where the surplus unburned  mixture goes to when it's pushed back out of the inlet valves.

[Mr Vlad]

Comedian. You state you have dyno charts for bikes. My heart is in motorbikes. I can't comment on your dyno charts because bike engines are so much different But better than car engines. 

On a TV programme called Fifth Gear they did rolling road tests on the same car to compare standard and premium fuel. Premium fuel came out best.

As for the Atkinson engine fitted to our is300h's all I state is My experience which comes from well over 100's of thousand miles of car travel. My car runs better. Sweeter and more economical. 

Someone mentioned that a 1/3 tank of premium has no effect on 2/3 of standard. Sorry pal my experience tells me different. Oh I'm a truck driver having done near 1 1/2 million miles in my time. I know what I know from a shed load of experience. 

Happy driving.

[ColinBarber]

1 hour ago, reeac said:

What I don't understand is where the surplus unburned  mixture goes to when it's pushed back out of the inlet valves.

In the case of the IS300h it is mainly air that is pushed back into the inlet manifold and the piston that is on it's intake cycle will draw it in. Most of the fuel is added at the top of the compression cycle through the direct injection system (I say most because the engine also has port injection too).

For the NX300h, which isn't direct injection, only port injection, it will be the correct ratio of fuel and air that is pushed back. The injectors will only add only enough additional fuel for the additional fresh air drawn in to get the overall mixture correct.

Also remember that these engines have variable valve timing, the effective compression ratio is increased at higher rpm to something much nearer the actual compression ratio when maximum power is required.

[ganzoom]

7 hours ago, Mr Vlad said:

Oh I'm a truck driver having done near 1 1/2 million miles in my time. I know what I know from a shed load of experience. 

Don't underestimate the human ability to make totally wrong assumptions and decisions based on 'personal experience'.

How similar is your truck to a Toyota hybrid drivetrain?

In your 1.5 million miles of driving how did you come to your conclusions? Were you blinded to the type of fuel you used? How did you control your variables and account for bias?

https://www.usatoday.com/story/money/cars/2016/09/20/buying-premium-gas-when-you-only-need-regular-youre-wasting-your-money-says-aaa/90726998/

[Mr Vlad]

Hi Ganzoom. The trucks I've driven are not similar to Toyota's hybrid system in any way. My conclusions come from experience. One company I worked for changed to premium fuel after I proved by getting 80 miles more to the tank. At that time it was cheaper to change (3 years ago )

That link you posted is American. Their fuel is a bit different to ours I believe and the AAA have been proved wrong a few times over the years. Don't ask me how it'sjust what's in my memory banks.

Like I've stated very clearly. It's down to the individual. There are millions of us who like to use premium fuels. End of.

[Thackeray]

20 hours ago, ColinBarber said:

Also remember that these engines have variable valve timing, the effective compression ratio is increased at higher rpm to something much nearer the actual compression ratio when maximum power is required.

That's interesting. Thanks for the explanation.

[Guest]

I'm just going to leave this here:

Quote

Good Afternoon,

 

Thank you for contacting Esso Customer Care.

 The majority of unleaded 95 Octane petrol sold in the UK contains 5% ethanol as required under the Government’s Renewable Transport Fuels Obligation (RTFO). 

 There is currently no requirement for renewable fuel (such as ethanol) to be present in super unleaded (97 grade petrol).

 I would like to inform you that Esso Energy Supreme+ Unleaded (UL 97) has a higher Octane than the regular grade. Esso Energy Supreme+ Unleaded additionally also has double the amount of our performance additive vs. Esso Energy regular unleaded (UL95).

Higher Octane fuel is only required for high performance vehicles that need a higher compression ratio in order to prevent knocking in the engine. Using higher Octane fuel will therefore not improve mileage in non-high performance petrol vehicles.

 The Esso performance additive does improve vehicle performance in the long run as it helps clean up deposits that are formed on the tips of fuel injectors. The double dose rate in the Supreme+ Unleaded gives a deeper clean compared to the regular dose rate used in the regular Unleaded. The nature of these additives is such that mileage improvements cannot be seen instantaneously at the current time but only over a period of time (min. 3 months). Esso is currently working on developing additives that can provide instantaneous improvements in mileage and with those we would be able to report the expected improvement in fuel economy more accurately.

If you need any further information, please feel free to let me know.

 

I was asking about ethanol but they went into Octane just for fun I guess. 

 

[parkman]

Interesting discussion, this. It interests me because I use BP 98 octane in my 1983 Mercedes 500se, which is a 5 litre V8. 

I found that the motor is noticeably livelier using 98 as opposed to 95 octane. Whether that difference would carry over to a 2013 IS 300h is perhaps difficult to ascertain. The Merc has a fairly basic fuel injection system and just likes to get fed good old fashioned high octane petrol !!!

Parkman.