Support the channel by shopping through this link: Become a member: @d4a/join Patreon: HCCI combines the benefits of both gasoline and diesel engines but without any of the drawbacks. It's as efficient as diesel but as clean as gasoline. However, there is a catch. The hidden problem of HCCI is control. Both gasoline and diesel get to decide exactly when combustion occurs. Gasoline engines have full control over the spark plug and Diesel engines have full control over the injection. But HCCI is based around the spontaneous auto-ignition of the air-fuel mixture, which means that it ignites when it ignites. Of course, this means that the point of ignition changes as engine conditions and loads change. Consistent and reliable cold starts are now more problematic. Changing loads are super problematic. We want more fuel in the cylinder to create more power for high loads and we want less fuel in the cylinder to save fuel during cruising. But different air fuel ratios auto-ignite at different times, leading to very unpredictable engine behavior. Ultimately, to control HCCI reliably, we would need to know the exact amount of air and fuel atoms as well as cylinder pressures and temperatures moment by moment as the engine operates in order to reliably control a HCCI engine. Despite all our technology, we are not yet able to do that. That’s why Mazda said, hey, we’ve been thinking about this all wrong. Let’s do HCCI but let’s also keep the control. They called it SPCCI or spark-controlled compression ignition. Everything is nearly the same as HCCI except the spark plug. The engine uses gasoline. It has a 16.3:1 compression ratio which is the same as modern diesels. It also runs at very lean air-fuel mixtures. The spark isn’t used to ignite the entire cylinder. Instead, a very small amount of fuel is injected locally right at the spark plug near the end of the compression stroke. The spark ignites this miniature local fireball and then this mini combustion raises the pressure and temperature of the entire already hot and compressed cylinder to the point that the remaining air and fuel auto-ignite. When running on SPCCI, Mazda’s engines are capable of 30% reduced fuel consumption compared to conventional engines. However, SPCCI is mostly limited to cruising and constant low and medium load scenarios. Stuff like highway driving. In other words, the engine is not capable of running in SPCCI all the time. High load and stop and go traffic it will behave mostly like a conventional gasoline engine. Despite this, it is a crucial breakthrough. It is the worlds frist mass produced engine capable of reliably achieving compression ignition. It is the first real step on the road to full HCCI. Mazda calls these engines Skyactiv-X and this is not news, this engine has been introduced in 2019, it has been on the market for 6 years already. And I’ll be honest with you, when Mazda first introduced this to the market a part of expected they would fail. 16:1 on a gasoline engine, compression ignition, very clever and complicated electronics. It is a complex engine and so I felt that chances were high there’s going to be a big embarrassing recall somewhere down the road. But 6 years later. No recall. In fact, these engines have proven themselves to be reliable. Much more reliable than the vast majority of downsized turbocharged engines employed by nearly all other car manufacturers. Despite this, 6 years after the introduction of this technology none of the other manufacturers have made any attempts to make their own version of it. Mazda has proven that it can be done. They have proven there are benefits. They have proven it can be made reliable. But nobody else has done it or is trying to do it? Why? I’m sure that money isn’t the problem. Mazda is actually a small manufacturer with a R&D budget that is smaller than that of most other big names. Toyota, Volkswagen, Ford, Hyundai and many others all have the R&D and engineers to make their own version of HCCI. I’m sure that some would love to make a less reliable version of it too……. The technology also isn’t prohibitively expensive which is reflected by the reasonable price of Mazda cars equipped with skyactiv x engines. It must be the upcoming EV revolution then? Seems a bit slow for a revolution, as combustion engines still make a very large, very gradually decreasing portion of the market. And there’s no doubt that there would be many benefits in combining spcci engines with various levels of hybridization. A special thank you to my patrons: Daniel Peter Della Flora valqk Dave Westwood Zwoa Meda Beda Cole Philips Allan Mackay Sam Lutfi Alex 00:00 HCCI vs Gasoline vs Diesel 07:38 How Mazda does HCCI - Skyactiv-X SPCCI 09:29 Why isn't it catching on? #d4a #mazda #skyactiv-x