Homogeneous charge compression ignition

Mazda Skyactiv-X HCCI Engine Technology Explained | AutoExpert John Cadogan | Australia

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• published: 09 Aug 2017
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Mazda announced yesterday that it would deploy - in production - the biggest advance in petrol engines since the carburettor in the fiscal year ending in March 2019. That’s according to Kiyoshi Fujiwara, the Director and Senior Managing Executive Officer of Mazda. He’s the big cheese of R&D; basically. The advance is compression ignition for petrol engines - I spoke about it to you earlier in the week - and if you did not watch - shame on you. Subscribe now to avoid similar embarrassing incidents in the future. Compression ignition represents the biggest step forward for petrol engine efficiency … certainly this century. Maybe ever. Credit where it is due - this development firmly cements Mazda as the leading internal combustion engine innovator on Earth. This is a big deal - we’ll get into the technicalities in a minute - to the extent that they are public, at least. They’re calling it Skyactiv-X, and it basically means a two-litre engine with the technology performs (quote) “better than 2.5 litres with lower fuel consumption than 1.5 litres”. Kiyoshi-san - Mazda’s R&D; bigwig - says the compression ignition technology delivers 30 to 45 per cent better fuel economy than an inline four from 2008. He also says it will offer the same economy as a Skyactiv diesel engine - only burning gasoline. This is a huge deal. It really is the holy grail of combustion management. It’s not unlike what happens in a diesel engine. In a modern diesel you squirt fuel into compressed air at high temperature. It autoignites. No spark plug, obviously. They call that ‘stratified charge compression ignition’ or SCCI. Squirting the diesel in? That’s the ‘stratified’ bit. The petrol process is subtly different. The fuel is mixed with the air. (This is the key difference to diesel.) Then it’s compressed and autoignites. They call that ‘homogeneous charge compression ignition’ or HCCI. The ‘homogeneous’ part is: It’s all mixed up, then it burns. The basic advantages for a petrol engine are: You get to use a higher compression ratio. That allows the fuel-air mixture to expand through a greater range when it burns, delivering fundamentally greater efficiency. Because of the homogeneous mixture and the fact that it’s the compression doing the igniting, the ignition occurs everywhere in the chamber simultaneously - rather than radiating out from a spark plug. And that greatly increases the load on the piston, which is where the useful work that the engine does actually comes from. It also reduces the peak temperature of the process, which slashes the production of oxides of nitrogen - the class of gasses that got Volkswagen into such deep doo-doo. And it doesn’t produce carbon nanoparticles, either. But wait - there’s more: It also speeds up the combustion process. So it sounds perfect - almost too good to be true. And in a sense it is - at least in terms of the problematic feedback, if you’re an engineer trying to make the system work reliably. Plenty of manufacturers have dipped their toes into that with varying degrees of success.