Hello everyone and welcome. In this video we're gonna be talking about a very cool
type of combustion, which uses gasoline and diesel fuel in the same engine and in labs has been shown to achieve thermal efficiencies
of 60%. So it's called RCCI,
reactivity controlled compression ignition, and that's what we're gonna be talking about in this video.
I know this looks like a ton of information
but it's gonna be a great general
overview of how this engine works.
A lot of the research for this engine has come out of the University of Wisconsin, so shout out to the University of Wisconsin
for the work that they've done on this very cool stuff.
So first we're gonna get into the engine, then we will talk about how
combustion works.
We'll get into some of the finer details about you know different loads,
thermal efficiencies, air-to-fuel ratios, that kind of thing. Then get into finally the pros and cons of the engine toward the end.
So how does the engine work? Well the whole idea is that you have two different types of fuel: one with a low reactivity
and one with a high reactivity. So in this case we have a port injector
which will be injecting gasoline (you can choose to use other different fuels, they've tested out natural gas and ethanol as the low reactivity fuel),
and then you have direct injection of a high reactivity fuel, in this case diesel fuel.
So diesel fuel has a short ignition delay: the time that it takes from when that fuel is injected to when it ignites.
And it wants to ignite in those conditions versus the gasoline (which) doesn't want to ignite in those conditions
it has a lower reactivity. And so that's the basic structure of the engine
where you're going to have two different types of fuel: one with high reactivity one, with low reactivity.
It doesn't have to be gasoline and diesel, but that's what in this video
we're talking about, and that's what a lot of their testing involved was using gasoline and diesel fuel.
Okay so how does
combustion occur within this engine?
So we're gonna go through the steps that take place.
Of course the first one being you've got that port
injector so during your intake stroke as that piston is moving down
pulling in an air fuel mixture of gasoline and air.
Then it starts to compress and there are going to be two injections
of diesel fuel. So the first one is injected
before that air fuel mixture has gotten very hot so it's not hot enough to ignite that fuel.
And it's going to start mixing that diesel fuel with the gasoline kind of creating this kind of layer, this area right
here which is a mix of gasoline and diesel fuel, versus just
gasoline which will be around the outside so that's going to start to mix in and then as that piston gets closer to the top
then you're going to be injecting a little bit more diesel fuel which is used purely for ignition
and you could inject a bit more actually for the air fuel ratio
but you're doing that final injection to start
combustion so what happens with that second injection is you have what is called a cool flame, so it's a diesel cool flame
and it's just the diesel fuel that has been injected. That's starting to ignite
not that you know mixture of gasoline and diesel fuel and so there's a little low
reactive just on that very edge of that fuel that's injected in a very small you know cool
flame is what it's called because there's not a lot of heat that comes out as a result of it
but it's enough heat to start combustion and the rest of the chamber
so once that cool flame has started that forces the diesel and gasoline mixture
which is around it to then ignite
and then once that diesel and gasoline
mixture starts to ignite that of course causes the gasoline which is around the rest of the cylinder to ignite
so that's kind of the three-step process you have that cool flame
you have the mixture that ignites, and then you have the gasoline that ignites
and so if you look at a pressure curve so here on the bottom. We've just got
degrees of the crankshaft rotation so zero would be top dead center negative 10 will be 10 degrees before top dead center
and so you can see first you've got that cool flame
which causes a little pressure rise then you have that mixed area which starts to ignite?
and then you have finally another pressure bump once that gasoline ignites, so that's the process of combustion and
depending on how you change the ratio of diesel fuel to
gasoline this curve will change pretty dramatically ok so now let's talk about some test results and some you know data
surrounding real engines using this style of combustion so in this case we're gonna be talking about a 2.44 liter
single cylinder. This is a heavy duty engine so it's just a single cylinder 2.44 liter
caterpillar Scot engine with a compression ratio of 16.1:1 operating at 1300 rpm they also did testing in a
1.9 Liter GM four-cylinder engine just to prove that it can be used light duty and heavy duty applications
but the results we're discussing here are from the single cylinder 2.44L
and so we're gonna be talking about the gasoline percentage the air fuel ratio
and the thermal efficiency and basically the way this test works is they hold the engine constant at
1300 rpm and then they vary the load, so essentially how much throttle it's getting so very low throttle to full throttle and
measuring different points the gasoline percentage air fuel ratio and thermal efficiency at these different points
and so of course you know what what you're doing essentially is you're taking that dyno
and it's braking the engine as the load increases to make sure that the RPM stays at 1300 rpm
but the load can vary and so starting off with the gasoline percentage at lower load
you use less gasoline and part of this is because gasoline resists ignition at low loads
it's one of the reasons why HCCI engines which are kind of like the Holy Grail are so difficult is because
they it's hard to have low load gasoline auto ignition
versus you know in this engine you're using two different fuels and you're using
diesel fuel as your ignition source so you can get away with using
gasoline at low loads and things like that but essentially as you increase in load you increase the percentage of gasoline
and that's not a perfect correlation
there's kind of a sweet spot in there, and then it dips back down and comes back up
but essentially at lower loads you're using less gasoline more diesel fuel at higher loads
you're using as much as 90% gasoline with just 10%
diesel fuel and most of the time you're going to be injecting most of the diesel fuel in that first injection
so the one that mixes
but some points you know in this load range you actually do inject more diesel fuel in that second injection
so it's there's a lot going on control wise while this is happening while you're sweeping that range of
the engine within that set rpm so the air fuel ratio as you might expect
is very high at low load and then it gets lower so once you're getting to you know
majority, gasoline of course you've got to get that air fuel ratio down much lower
but when you've got that mix of diesel fuel and gasoline very cool
you can actually operate at this forty five to one air/fuel ratio
so at low load you can get you know super good fuel efficiency because you're using a really high air to fuel ratio and
you know you're not using too much fuel of course because you're at low load your efficiency is still high
so that's kind of what the coolest thing about this is is that the thermal efficiency
worst case on this chart right here is 49%
and of course you know this is a pretty efficient rpm as you get into higher rpm the efficiency will start to decrease
but what's very cool is that across the entire load range your worst case scenario is 49% thermal efficiency
and you know kind of peaks in the center here at
56% thermal efficiency so for context Mazda's SPCCI engine which is super efficient,
currently they're SKYACTIV X engine which is an on sale yet
is peaking somewhere around you know forty three ish percent. They haven't released actual numbers, but they've said it's slightly better than the best
that's out there. Which is in the Toyota Prius which is around forty two percent now diesel engines will have better efficiency
they'll tend to be you know in the forty eight close to 50 percent region
but this is exceeding diesel efficiency so very cool
what's possible using the combination the best of both worlds between gasoline and diesel.
Okay so that leads us to pros and cons and one of the things we haven't even discussed in this video is the huge benefit that
this engine has which is emissions, and so it has very low
nitrogen oxide emissions and very low particulate matter so soot and you know this is kind of a trouble, a burden on diesel engines
but because this has very cool burning it doesn't produce the nitrogen oxides and
because the diesel fuel has time to mix and because you're not using a lot of that diesel fuel
most of your fuel is mixed well mixed and well mixed fuel doesn't tend to produce particulate matter
it's where you have those rich pockets of fuel that produces particulate matter so particular matter and
nitrogen oxide and OX
emissions are very very low in this engine and so that's a huge benefit of it aside from the fact that it's extraordinarily
efficient so super efficient ten to fifteen percent more efficient than you know some of the diesel engines out there
and this is mainly as a result of having lower
combustion temperatures and because of that less heat transfer within
the cylinder so actually when they achieved in the lab the 60%
thermal efficiency one of the things they did is they didn't have oil cooling for the piston because they found out that that oil cooling
actually pulled out some of the work. That was being done
you know from combustion
so you know a you know a method that they used in order to slightly improve the efficiency there
but they were able to achieve 60 percent thermal efficiency in lab testing so very cool to see
eliminate exhaust after treatment, so that's a really cool thing that they were able to do based on 2010 EPA requirements
they were able to meet those requirements without any exhaust after treatment
which of course everything that's diesel is using exhaust ever after treatments to take care of it if they're doing it correctly
and so you know pretty
interesting that there is a way that you could possibly get around that and if you could you could save a ton of money by
not having all that expensive equipment in the exhaust
required for diesel engines today so some of the disadvantages well two fuels
obviously is an ideal for a consumer
you don't want to have two separate tanks to fill up then you've got two separate fuel systems to worry about
so that kind of is you know a disadvantage to think about also you know there are there
are there is research occurring in which you're only using one fuel and then either treating it or
kind of getting into some different methods at which you can use a single main fuel tank and either add additives or
manipulate that fuel somehow so you can still have this kind of combustion method so perhaps
i'll do a video later on talking about something like that
and of course, this is a development engine, so there's plenty of kinks to work out. It's still being developed
it's not mass-produced
so it's not as simple and amazing as this you know short little whiteboard video makes it seem
there are definitely challenges with it. I also think you know if you're going to have a peak efficiency without oil cooling
that's probably not ideal unless you've got pistons that can somehow handle not having that oil
cooling or that 60% thermal efficiency was achieved, but regardless you know they they are able to achieve
56% you know pretty easily so it's a truly and very cool
efficient method of combustion if you guys found this interesting
I will certainly include some related videos of other different styles of combustion and their benefits
and also I will include some research which kind of shows
you know behind you can go into the research that this video is based off of if you care to check that out the
language will not be quite as nice as this video
you're gonna get all kinds of crazy acronyms and that kind of thing, but if you'd like to check it out
i'll certainly include links to it.
So thank you all so much for watching, and if you would like to leave any questions or comments feel free to do so below.