S*******r
发帖数: 64 | 1 这个话题其实不仅限于MDX， 这里只是用MDX为例。我觉得许多人都对这个问题似是而
非，网上也有很多讨论和和解释。多数都没有讲得非常清楚。最近读到这篇文章， 作
者是skirmich。他从原理和设计的角度解释了为什么【in any High Compression
Engine included the new Honda engines that only “Recommend" using Premium
but does "Not Require it“】。我觉得这篇文章可以帮我们澄清一些疑问，贴出来与
大家分享讨论，可惜原文是英文，作者在里面也回答了一些网友的疑问， 比如MAZDA
的不同设计。
链接如下：
https://www.mdxers.org/forums/68-fuel-octane-mileage-etc/126946-premium-vs-
regular.html
以下是复制粘贴的原文和作者对一些问题的解答。
----
Premium vs Regular
Hi!
Before you think this is another "pro using Regular" thread don't worry this
isn't one. Instead I want to explain in a simple common man words why you
should be using PREMIUM in the MDX or in fact in any High Compression Engine
included the new Honda engines that only "Recommend" using Premium but does
"Not Require it".
WARNING: If you don't like to Read then this is not for You.. But if you
take your time to read through all this word fest you might learn something
new and save money in the end. I had some free time and wanted to explain
this in detail and in an easy to understand manner.
First the Basics:
What is Premium Gas? Premium is just a fancy way to call a high octane
gasoline this means that premium is a gasoline with +91 octane.
What is Octane Rating? The Octane rating states how difficult it is to
ignite the gasoline but you may think why would you need a Gasoline that is
hard to ignite? Well this has to do with Compression.
What is Compression? Compression is when the Air and Fuel mixture is
compressed in the combustion chamber this is calculated by the
Stoichiometric ex: 11:1, 12:1, 13:1, 14:1 which means that the mixture of
air and fuel is compressed a lot, This is referred as High Compression.
Gasoline stoichiometric ratings for compression stop at 15:1 this is because
only Gasolines with Higher Octane ratings (+100 Octane) can handle such
compression. Since those gasolines aren't mainstream made engines use the
most out of 91 and 93 octane which has a maximum stoichiometric of 14.5:1
These numbers refers to the amount of air vs gasoline that enters the
combustion chamber, Having very little gasoline per air volume creates a
Lean Mixture which in turns creates a LOT of heat.
The advanced stuff:
Honda Engines.
Honda since the very beginning is trying to make the most out of the
displacement of the engines they make, by making high compression engines
they can take the most out of the Combustion Stroke without using as much
fuel. This is why most if not all their engine are High Compression Engines.
What about Regular?
Regular gasoline has an octane rating of 87 which means it can pre-ignite
faster than Premium. Now that you know that High Compression engines run
hotter this means that Regular fuel can pre-Ignite before the compression
stroke ends.
What happens when the engine pre-Ignites?
Knocking, Ping or Detonation they are all results of pre-Ignite. What
happens is that the engine is turning clockwise, the compression stroke
builds up and when ignition occurs the piston is pushed downwards to keep
the crankshaft turning clockwise. If Regular fuels pre-Ignites before the
compression stroke can end it will fire up then the Piston is moving Upwards
which then will be pushed Downwards causing the crankshaft to force it to
turn counter-clockwise. This will cause SEVERE Damage to the Piston Rod
which is pushing the piston upwards.
How come my Honda Engine can run Regular then if its High Compression Engine
?
Since the dawn of Computer Controlled Ignition (PGM-FI) the ECU (Car
computer) can control when to fire the spark plug, how much gasoline enters
a combustion chamber and know when the engine is going to pre-Ignite. What
the ECU will do in this scenario is simply put retard Ignition thus Timing.
What is Retard Timing?
Timing is referred to the exact moment the valves closes to start the
compression & ignition stroke, the ECU can use the spark plug and timing (i-
VTEC) to reduce the combustion chamber HEAT this is done by opening the
exhaust valves sooner during the ignition stroke and by igniting the spark
plug as late as possible (VTEC) so part of the combustion can exhaust sooner.
What are then the consequences of Retard Timing?
An Engine with Late Timing has more wear on the exhaust valves since its
letting hotter combustion gasses pass through. This allows the combustion
chamber to run cooler in order to prevent Regular gas from self-igniting but
it also mean the Power Stroke is losing force thus the engine runs weaker
and less efficient.
So why am I using Regular in a Honda Engine?
You might think you are "Saving Money" at the pump but in reality you have
more wear and less MPGs using a Gasoline that technically is not made for
High Compression Engines.
Why Honda then is Pushing "Not Required" in the 3rd Gen?
Simply put because of Demand and Supply.. People want to save money so if
you are cross-shopping 2 cars and one demands premium and the other not then
you have a higher chance of losing a sale.
What Honda did to make it able to run Regular on the 3rd Gen?
Honda engines can run Regular because the ECU can pull timing in order to
run less efficient but safe. At this point you might be thinking Perhaps my
3rd gen MDX does not have a High Compression Engine! and you are wrong.. the
J35Y5 has a compression of 11.5:1 making it a High Compression Engine.
This means it DOES require Premium because Regular is not meant to be used
in such environment's. This means that every time you fill up with regular
your engine is running less efficient and with less power than what Honda
states.
But.. The car feels fine running Regular?
Of course it does silly we already made clear that the car can Pull Timing
in order to run Regular!
But but.. People say I can run Regular if I don't WOT the car or Tow or Push
the Car?
This is true again because the ECU will pull Timing so it doesn't really
matter if you WOT (Wide Open Throttle = Floor It).
But but but.. People say that at lower RPMs Regular and Premium does not
make a difference, it only matters at High RPM?
This is not only silly but completely untrue, The Engine was designed to run
optimally with Premium in Mind this is becase again this is a High
Compression engine they need to make out the most of the displacement and
order to do that it needs Premium.
When the engine is running the ECU is trying to run the maximum compression
it can, this is how the engine gets those lovely MPGs. So when you floor it
the engine starts to hit an Air Volume Wall (Low RPMS) this is where VTEC
kicks in, It makes the Intake Valves open longer and thus adding more Volume
of Air which also needs more fuel to compensate and get that High
Compression that makes all the power.. This means Compression ALWAYS STAYS
HIGH! there is nothing like ohh yes when I am not flooring it, Regular is
totally fine! again the engine runs LEAN as much as it cans because this is
how you get MPGs. No one wants an engine using loads of fuel.
So if my Honda Engine is always trying to lean out to save fuel? What
happens if I am Using Regular at low RPMS?
It happens the same as all the power band, the ECU will pull the timing like
it or not. Lean = Hot = pre-Ignition Condition. So unless you make the
engine try not to give the best MPGs there is no possible way to make the
engine run efficient with Regular.
But if the ECU is preventing Knocking then its safe to use Regular Right?
But it is not normal to try to run the car in a less efficient way to save
money. Just look it at this way.. If the engine needs 10oz of fuel for 1HP
it means that using Regular the engine do 0.5HP for 10oz of fuel.. You are
losing power which means you need more gas to move the car.. Honda states
that the engine makes 290HP for the J35Y5 that is using PREMIUM! at low
speed you might not feel the difference since the engine makes those 290HP
at 6200RPM at normal Daily Driving RPM speeds its making way way less than
that. So if the engine already has a low output using the gasoline it needs
then using regular is making even LESS.
This requires to compensate by giving it more gas to do the same thing it
can make with less gas. In the end you are NOT SAVING MONEY by using Regular
on a High Compression Engine. Running Premium makes the engine run at its
optimum performance giving you the HP you paid for, Making it last longer
too.
This is the bottom line.. Its not what you THINK it is or how you THINK it
works because nothing bad has happened..
This is Physics, Thermodynamics and Basic Mechanics..
High Compression NEEDS Higher Octane Fuel.
Unless Honda starts making engines with a sub 10.0:1 compression ratio then
Regular is not the fuel you should be running on your +50,000 Dollar CUV.
This is why Low Compression Engines do not benefit from Higher Octane Fuel,
They wont make enough heat to ignite Premium efficiently and thus might be
ran less efficient running Premium than Regular a Good example is the HEMI 5
.7L that states NOT TO USE PREMIUM BECAUSE IT WILL LOSE POWER.
PLEASE Do not said you are getting more MPGs out of Regular on a High
Compression Engine this is Physically Impossible. You can run Regular on the
car because ECUs are that smart and avoid a catastrophic failure but in no
way shape or form a 11.5:1 Engine was made to be ran on Regular... Any
engine that has that high of compression is pulling timing running Regular
on daily basis.
--------------------------
Q：（wuryan）
ood summary and totally agree.
I have always used premium in all my previous cars
but my 2016 MDX doesn't seem to care or run any differently on regular vs
premium.
I always test it out for about 2-3 tanks of each to determine what fuel I'm
going to use for my car. and to my surprise, MDX runs pretty much the same
on cheaper gas. Vastly different results from my same generation RDX.
Something funny's going on here.
A：That can probably be because the ECU is tuned to give different shift
points when using Regular to compensate. Older cars where not tuned to run
differently with Regular and that is why the lower performance was more
obvious.
In any case Honda is still protected because it "Recommends" to use 91..
Q：（bigheadwillie）
Not all high compression engines require premium.
I have a question about this part of your post: "Unless Honda starts making
engines with a sub 10.0:1 compression ratio then Regular is not the fuel you
should be running on your +50,000 Dollar CUV. " . If the requirement for
Premium Fuel is purely based on the compression ratio, then why is it that
my previous car (2015 Mazda 6) had a compression ratio of 13.0:1 and ran on
87 octane gasoline? That was the fuel recommended by Mazda.
A：As mentioned above Skyactiv works very differently.. Mazda actually
pushed the technology to allow the use of REGULAR on a High Compression
engine..
Difference is, Honda/Acura has not done anything of the sorts.. Its entirely
relying on the ECU ability to pull timing to allow the use of Regular..
Mazda designed the Skyactiv to USE Regular not as an after thought.
Honda & Acura is not "Requiring" Premium is due the ever more strict CAFE
Standards and the most compelling reason: Because it will sell Cars...
Q：（DaveW2）
When I saw this I first thought, great, a thorough discussion on why we need
to use 91 octane gas. But when you conflated compression ratio with air-
fuel ratio, it was clear that you don't really know much about engines.
Compression ratio is cylinder volume at the bottom of the stroke divided by
cylinder volume at the top of the stroke. Air-fuel ratio and stociometric
mixtures are a totally different parameter.
A：Its funny because I didn't want to go into debate, the idea was to
explain in a very simplistic matter to people that do not even know what air
fuel ratio and stoichiometric is, Why they should be running Premium..
I think DaveW2 should know anyone that knows the difference would not even
try Regular on their MDX, So its not even up to debate. |
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