Mazda's sparkless gas engine 2018

[petemarovic]

How? How? How?? How does the fuel ignite spontaneously? How does it create more power? How does it burn more efficiently?

Is it a higher compression ratio? Does it work the same with different grades of gasoline? What are the drawbacks? Why not go all-in with the technology?

Might as well say, "Mazda is putting a new engine in their cars. This car's a pretty red one."

[NL_Fer]

They use “knock” to auto ignite the mixture. They use high compression and a supercharger to increase mixture temp to just under auto ignition. Than they use the direct injector and sparkplug to ignite a small puff of gasoline. The shock caused by the ignition of the gasoline causes the main mixture to auto ignite. So it is auto ignition triggered by shock, instead of combustion by a growing flame front caused by the spark.

[Smokes]

You should also remember this technology was being developed in the 1980's to reduce emissions but the government legislation killed the development off, by mandating the use of more expensive catalytic converter and fuel injection in the early 90's.

[NL_Fer]

You should also remember this technology was being developed in the 1980's to reduce emissions but the government legislation killed the development off, by mandating the use of more expensive catalytic converter and fuel injection in the early 90's.

Those were also lean-burn engines, but definitly not auto-igniting. If u refer to Honda CCVC, that was a stratified charge, where the rich part was ignited by a spark, but the rest was burned trough a flame front or several flames. Auto-ignition is where pressure and heat is causing the mixture to ignite by itself.

[gambler]

How do they get that much fuel into the chamber that quick and still get an even mix? Multiple injectors? Supercompressed fuel? This also lends the notion low octane fuel may be used, however it does make me wonder about rpm increase with higher octane. I like the general idea and would not be surprised if it is not already being used in spark engines to combat preignition.

[ziggy]

Its Spark Controlled Compression Ignition (SPCCI) or better Spark Assisted Compression Ignition (SACI). The HCCI part can happen only under special circumstances and is so "sensitive" that even a ambient temperature change can disturb it. Thats the time where the spark plug comes into play. There are tons of info on the net, just google it.

Personaly I am pretty sure F1 is using it or at least a form of it. Maybe only some manufacturers and some not?

[ziggy]

You should also remember this technology was being developed in the 1980's to reduce emissions but the government legislation killed the development off, by mandating the use of more expensive catalytic converter and fuel injection in the early 90's.

AFAIK they couldn't make it work because they didn't have in-chamber pressure sensors. In the 2000s these sensors became available and the progress continued. These complex sensors are the base for such combustion...

They use “knock” to auto ignite the mixture. They use high compression and a supercharger to increase mixture temp to just under auto ignition. Than they use the direct injector and sparkplug to ignite a small puff of gasoline. The shock caused by the ignition of the gasoline causes the main mixture to auto ignite. So it is auto ignition triggered by shock, instead of combustion by a growing flame front caused by the spark.

The spark isn't used at all times. Only when it's needed. Only 1 Knock event can damage the sensors mentioned above, so I'm not sure what to think about it.

Christian Horner said in an interview that these sensors cost 15k € or so and get damaged after only 1 knock event. Another indication of SACI.

[NL_Fer]

Nope, wrong.

Mazda SPCCI uses the spark to ignite a rich part of the not so homogeneous mixture, then the shock of this ignition triggers auto-ignition of the lean part of the mixture. This way the spark is used to exactly time the igniton. This to prevent unwanted pre-ignition or knock.

Basicly this is knock, but the exact timing and single combustion prevents damage.

[etusch]

[etusch]

When Mazda developed its Skyactiv-X Spark Controlled Compression Ignition (SPCCI) engine, it perfected one of the most elusive concepts since Nikolaus Otto’s first thumper clanked into life nearly 150 years ago. Why? Getting petrol to ignite in the same way as a diesel by compression instead of a spark had been an engineering holy grail for a long time.

Auto Ignition, Combined Combustion System and Gasoline Compression Ignition are all names used for similar past projects by others attempting to perfect the same concept. The proper name for the underlying concept behind all of these (including SPCCI) is Homogeneous Charge Compression Ignition (HCCI).

With HCCI engines, the fuel is evenly – homogeneously – mixed in the combustion chamber. It’s lean, too, with extra air supplied by a supercharger-like pump. Compression ignition exploits the fact that if you squeeze air enough, it gets hotter (try closing the end of a bicycle pump with your thumb). It’s how sparkless diesels work and why they need a much higher compression ratio than petrol – and it’s why some billed the HCCI concept as the merging of petrol and diesel engine technology.


But why bother and what are the advantages? Plenty, according to many industry gurus. When fired by HCCI, the fuel air charge ignites as a whole throughout the combustion chamber. In a conventional spark-ignition petrol engine, fuel is ignited at the spark plug and then spreads along a flame front. The benefits of doing it the HCCI way include reduced fuel consumption and CO2 emissions and fewer oxides of nitrogen (NOx).

Back in 2001, Lotus Engineering developed a system where the fuel was ignited by hot exhaust gases re-ingested into the engine, to achieve much the same goal as Mazda. Ricardo also produced research engines, and in 2007 Volkswagen demonstrated its prototype Gasoline Compression Ignition engine based on a FSI petrol engine. Like the Lotus concept, it used high levels of exhaust gas recirculation (EGR) to ignite the fuel.


HCCI using hot exhaust gases could only work when the engine wasn’t under much load, because of the smaller amounts of fuel used. For starting and full power, it needed a conventional spark, and a smooth switch between the two proved difficult to achieve.

SPCCI might sound like a cheat – after all, it still involves a spark. But the difference is the spark is used to ignite a small, fuel-rich ‘detonator’ charge injected directly around the spark plug. The rest of the chamber contains a lean charge brought to the brink of igniting by high compression. When the detonator charge is ignited by the spark, the expanding fireball from it increases enough extra pressure on the main charge to make it spontaneously combust. The pay-off is that SPCCI works when the engine is at full gallop and not just a gentle canter – so during most normal driving. The difference between this and the earlier concepts is that combustion is guaranteed and stable. You might say it’s a spark of genius.

What is lean burn?
Lean burn simply means lots of air and less fuel. In a petrol engine, the perfect mixture to achieve complete combustion of the fuel is 14.6 parts of air to one of fuel (14.6:1). The Skyactiv-X engine has a Rootes-type supercharger on the front of the engine, not to boost power but to provide enough air to burn much leaner at over 29.4:1.

https://www.autocar.co.uk/car-news/tech ... combustion

[etusch]