The Development of the SkyActiv-G Engine: A Breakthrough in Ultra-Efficient Internal Combustion

The development of the SkyActiv-G engine represents a significant breakthrough in the quest for ultra-efficient internal combustion engines. This innovative technology has been years in the making, and its release marks a major milestone in the pursuit of fuel economy and performance. The engine's creators have employed a range of clever techniques to achieve this goal, including the use of Spark Controlled Compression Ignition (SPCCI).

SPCCI is a method that combines elements of both diesel and gasoline engines. In a traditional gasoline engine, spark ignition occurs at the top dead center of the cylinder, where it ignites the air-fuel mixture. However, in an SPCCI engine, the spark plug fires earlier than the piston reaches the top dead center. This technique allows for more efficient combustion, as the pressure inside the cylinder builds up before the spark is applied. The result is a faster and more efficient combustion process.

One of the key benefits of SPCCI is its ability to improve efficiency in a wide range of operating conditions. Unlike traditional gasoline engines, which can suffer from reduced performance at high engine loads or low temperatures, the SkyActiv-G engine can maintain its fuel economy and performance characteristics even when subjected to extreme conditions. This makes it an attractive option for drivers who frequently encounter challenging weather conditions or drive in urban environments.

Another innovative feature of the SkyActiv-G engine is its use of a pressure sensor on top dead center. This sensor monitors the pressure inside the combustion chamber, ensuring that the spark plug fires at the optimal moment to achieve complete combustion. The result is a more efficient and responsive engine that produces fewer emissions.

The development of the SkyActiv-G engine has resulted in significant improvements in fuel economy compared to traditional gasoline engines. In class-leading tests, the new engine achieved fuel economy gains of 20%, making it an attractive option for drivers who prioritize efficiency without sacrificing performance.

One of the most exciting aspects of the SkyActiv-G engine is its ability to operate efficiently at a wide range of engine loads and RPMs. This means that drivers can enjoy improved responsiveness and agility, even when driving aggressively or in challenging conditions. With its advanced technology and innovative design, the SkyActiv-G engine represents a major breakthrough in the quest for ultra-efficient internal combustion engines.

The SkyActiv-G engine's creators have also emphasized its importance of delivering an enjoyable driving experience while maintaining exceptional fuel economy. Unlike some highly efficient engines that can sacrifice performance and responsiveness in pursuit of efficiency, the SkyActiv-G engine is designed to provide a lively and engaging driving experience.

I had the opportunity to drive one of these prototypes, which was powered by approximately 190 horsepower. While not extremely powerful, the engine's responsive nature made it feel more energetic than its advertised output would suggest. With aggressive gearing and advanced transmission technology, this prototype exhibited impressive acceleration and responsiveness, making for a highly enjoyable driving experience.

The development of the SkyActiv-G engine represents a major step forward in the pursuit of ultra-efficient internal combustion engines. By combining innovative technologies like SPCCI with advanced materials and design techniques, its creators have achieved significant gains in fuel economy while maintaining exceptional performance and responsiveness. As the automotive industry continues to evolve, this engine is sure to play a key role in shaping the future of transportation.

"WEBVTTKind: captionsLanguage: enHello everyone and welcome in this video we are talking about Mazda's revolutionary SkyActive-X engineit's really cool what they're doing with this and the basic approach is they're trying to you know determinewhat is the ideal engine and how do we get our internal combustion engine there?and I think the question will come up. You know why are they spending money and time?improving the internal combustion engine when the future will probably be electric and they are looking at hybridizing their vehiclesand they are looking at purely electric vehicles. They will be making them in the futurethey have said that that is in their plans to dobut that said there are still improvements which can be made to the internal combustion engineand I think kind of the proof of Mazda's logic with this is that for the past five yearsMazda has had the EPA's highest corporate average fuel economy rating for all manufacturersand that's without a single hybrid or electric vehicle so their approach is logical. You know they're improving somethingthey're making it better and they are overall reducing co2 emissions of the automotive world out thereand they're doing it better than pretty much everybody else without hybridizing or electrifying their carsthat's not to say that an electric car can't have better emissionsbut the way mazda is doing it is very smart for the time being so before we get startedinto, what are the specific changes? They have made to create this ideal engine or work towards this ideal enginehow does this engine work and so the premise of it is something called spark controlled compression ignition?so it's operating much more similarly to a diesel engine except that it's still using a spark plugso what you have happening is you have an air fuel mixture?and you're going to compress that air fuel mixture as much as you can without it igniting you want it to be justbefore it's about to ignite from pressure and heat alone and then right when it gets to that point you fire a spark plugthat spark plug creates a pressure wave and as that pressure wave expands outward it forces the rest of that mixturewhich is just before self combustion just from heat and pressure the pressure rises just a little bit more and then all of itsimultaneously ignites so similar to a diesel enginewhich it gives you a really high temperature and pressure area you spray in that fuel and it immediately igniteshere instead you have air and fuel you wait justbefore it's about to ignite fire a spark plug that in the pressure just slightly and then you have all of it combustsimultaneously, so that's the the methodology behind itbut you cannot always run it in this mode, soin you know the ideal conditions you want to run it with spark controlled compression ignition because the efficiency is greaterbut you can't always do that so if you're look at a graph of load versus rpmthere is going to be you know kind of a faded area where it switches from spark controlled compression ignitionto a regular spark ignition engine, so it operates just like any other gasoline engine out thereactually, it'll be running an Atkinson cycle when it's running on spark ignitionbut operating like a traditional gasoline engine the spark ignites the flame travels through that air fuel mixture you have combustion occurso there's kind of this you know shaded areawhich where it switches between the two the important thing to keep in mind is that it is always using a spark to control when?compression occurs, it's not going to have just purely compression ignitionit's always going to be using a spark in order to properly time when that ignition occursso now let's get into what are the ideal you know?what is an ideal engine and how did Mazda work towards that ideal engine?so an ideal engine has asuper high compression ratio as high as you can make it and mazda previously had the record in a production vehicle with the 14:1compression ratio for a gasoline engine and in the prototypes which I got to drivethey are running 16:1 so this will be very close to what ends up in the production enginesomewhere around 16:1 is where they found kind of the ideal scenarioand so this will be the highest of any gasoline engine out there. Now, what's the problem with high compression ratios?They give you more torquethey give you better efficiency, but they lead to engine knock and engine knock destroys enginesbut in this case we actually want engine knock occurring at the right time so it's not the same thingbut it's it's very similar so basically they want to control when knock occurs up instead of randomize knockthey want complete combustion of everything surrounding that entire air fuel mixture at the same time and what's cool aboutthis is they're running a 16:1 compression ratio with 87 octane fuel so regular octane gasthey actually found ideal was with 80 octane, but of course you know in the states 87 octane is the regular fuelthat's available so that's what they're choosing to use but a 16:1 compression ratio would never be paired with the lowest octane fuelin a different style engine and this one because they want knock to occur not exactly the same thing, but they want thatcompression ignition to occur a low octane fuel is desirableokay, so it has a high compression ratiothat's one thing another thing you want is lean combustion and thereason why you want lean combustion is lean combustion gives you lower flame temperatures it gives you less nitrousnitrous oxide emissions, and it gives you less energy lost as heat, so it means it's going to operate more efficientlyand so you know a lot of people say that as you lean out an air fuel ratio it burns hotterthat's not actually true. What happens is if you go if so herewe're looking at a plot of an air fuel ratio here would be a rich air fuel ratio here would be a very lean14.7:1 that's stoichiometric or the ideal air fuel ratiowhich means all of your fuel and air is burned completely so that's going to beessentially where your peak combustion temperature is and it's also going to be where your peak nitrous oxide emissions are occurring andas a result that's not really ideal from an emissions standpoint or from a combustion standpointbecause your temperatures are hot and you're producing a lot of bad emissionsso by leaning out that ratio the combustion temperatures start to fall and your nitrous oxide emissionsjust completely plummetand so there's there's a huge benefit if you can run it really lean and the way they do run it leanthere are problems with lean combustion and that is that lean burns slowly, and it burns kind of incompleteand so they have a very clever method where when that intake valve opensand the cylinder is pulling down it creates this swirl within the cylinderand that swirl helps to even out the ratioand then they also have directinjection and so they wait as that piston is coming upwards towards the top this has an air fuel ratio about37:1 which is unheard of in gasoline engines typically you're not going to see much higher than 16:1 something like thatideally, you know you're floating around that 15:1, so 37:1, 2.5 times the ideal ratioso as it's coming upthere's a direct injectorand that sprays a little bit of extra fuel which is right beside the spark plug so the area near the spark plug isless lean than the area of the rest of the cylinder so about 29:1 right beside the spark plug and then37:1 on the other areas the reason they do that is to help for thatspark controlled ignition to occur so the spark controlled ignition occursthen it starts to expand out and it forces the rest of this to combustsimultaneously so very cool what they've done. Now this is actually asupercharged engineso there's a supercharger on it Mazda calls it a leansupercharger and the reason why they call it a lean supercharger is because it's not to improve performance it canimprove performance a bit and they do use it slightly for thatbut the real reason why it's on there is to control the amount of air going into the enginethey want to be able to produce these super leanconditions where you have that air fuel ratio of 37:1 and that means a ton of air needs to get packed in thereand so that's why they use the supercharger and the benefit of running this lean combustion as mentionedyou've got less energy lost as heat from those lower combustion temperatures. You've got less nitrous oxide emissions andbecause you have extra air in there that extra air heats up during combustion and that basically multiplies the effect ofincreasing the pressure within the combustion chamber so you're improving the efficiency without necessarily using more fuel so it's a very clevermethod of getting super efficient combustion, okay, let's move on to our third ideal scenariowhich is instant combustion basically with an internal combustion engine you want that combustion to occurcompletely at up dead center all at once no delay whatsoever and so with a gasoline engineyou have a spark that fires, and then the combustion travels outward from that sparkand eventually burns up everything in there with the diesel engine it's much more instantaneous. It's much fasteryou spray in the fuel and immediately everything burns, so as you can see the in a diesel engineyou've burned up everything when the piston hasn't moved down all that much from top dead center versus in a gasoline enginethat piston is going to move down significantly more before all of the ar and fuel has been burnedso why isn't that ideal?well think about it this combustion is what's pushing your piston down,so if it combust at the very top that means it's going to be pushing your piston down the entire time if it's combustingtowards the bottom that means it doesn't have much time that it's going to be pushing that piston downso it's not doing as much useful work so with SPCCI. It's much similar to diesel ignitionyou have that spark fire, and then instantly everything else around it combustsso it's a much quicker combustion than a gasoline engine that improves efficiency and that also improves torquevery cool to haveso our final thing is combustion timing and as mentioned you want complete combustion to occur at top dead centerand you want that combustion to occur at top dead center so timing is the really tricky part here,which is what you know initially, why they chose to use a spark plug to control the compression ignitionso what's super clever about this engine,they have a pressure sensor on the top dead center, so it's not actually a spark in the top centerthe spark is a little bit offsetjust like the fuel injectorand they've got a pressure center up up top there and that pressure sensor ismonitoring the pressure inside of this combustion chamberand so if you look at pressure here on our vertical axis and the time you know basically our crank angle on ourhorizontal axis so where is that piston right here from here to here?it's during the compression stroke, so that's the time from the compression strokethis is the time for the power stroke, and then right here this green linewe have dead center, so your spark fires during that compression strokeand you can see that that causes the pressure to rise so that little bubble ofyou know combustion that's occurring is going to cause the pressure inside the cylinder to rise and you want that pressure to rise to theself ignition temperature of the air fuel mixtureso once it reaches that self ignition temperature and pressure then all of a sudden the rest of the cylinder combustsand you have a big peak in pressure, so you want that peak and pressure to occur?basically immediately after top dead center so that you get all the useful work out of ityou don't want it to be delayed. You know way after top Center, then you're not getting as much useful work andso the way that they control this what happens with if you have different humidity, different air temperature, different engine load, different rpm,things like that there's all kinds of variables that will cause how long it takes this spark to reach the self ignition temperaturefor that combustion pressure to get high enough for the rest of the compression mixto combust and so that timing is what's super-sensitive basicallyyou know all kinds of ambient conditions are changing this so that's what this pressure sensor is monitoringit's saying how long is it taking for the spark to fire and then compression ignition to occur and if it's taking a long time?it'll advance the timing and if it's taking a shorter amount of timeit'll push that timing back and so that way it's always using this pressure sensor to optimize that thisbig peak right here in pressure is occurring right after top dead centerso you get the maximum amount of performance and efficiency out of the engine.Very cool what they're doing all four of these are really exciting kind of methods of having thisapproaching towards the ideal internal combustion engine, so what are their results you know what is all this donewell the SkyActiv-G engine was class-leading that's their previousgasoline internal combustion engine was already class-leading in fuel economy, and they have increased its fuel economy by 20%and almost just as exciting if not more exciting than that is that it now operatesefficiently at a much wider load range and a much wider rpm range, so what does that mean?well you can be on the gas more and it can also use shorter gearing or more aggressivegearing so that you're at higher rpms, and you can get that response withoutsacrificing fuel economy so that's what's really cool about this engine you can be at higher rpms and higher engine loads than you would traditionallybe at and still be more efficientso that's it's it's really cool that it's going to be an engine that will have a lively characteristicI did get to drive it which was pretty exciting andyou know it's not a super powerful engine the prototype that I drove was about 190 horsepowerbut you know you have you can have more aggressive gearing with it, and you get response out of itso it leads for an engine that has characteristics that make it fun to drivei'm sure you could tune it for you know different horsepowersbut ultimately the idea behind it was to make this ultra efficient internal combustion engine, but it also doesn't sacrificeyou know the boredom that could be associated with a highly fuel economy highly engineered vehicle purely for fuel economyso thank you all for watching, and if you have any questions or comments feel free to leave them below.\n"