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Old 10th August 2017, 07:03   #1
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Default Mazda plans a new engine using both - compression & spark ignition

https://www.topgear.com/car-news/fut...bustion-engine

The engine fires using both compression (like diesels) and spark plug (like petrol mills), not sure just how they managed that.

I wonder just what fuel air mixture and compression ratio adjustment they worked out to manage this and not have the engine catch fire.

What do we have here, an engine that behaves like a diesel if you fill diesel and like a petrol if you fill petrol? One that runs on half petrol half diesel?
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Old 10th August 2017, 08:20   #2
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Default re: Mazda plans a new engine using both - compression & spark ignition

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Originally Posted by hserus View Post
What do we have here, an engine that behaves like a diesel if you fill diesel and like a petrol if you fill petrol? One that runs on half petrol half diesel?
Quite interesting and thanks for sharing.

From what I understand, it's a petrol engine that runs with very high compression ratios as seen in diesel engines. Usually, petrol engines run much lower compression ratios, or need high octane fuel when the compression ratios are increased (But still way short of the diesels) for more performance.

Without the high octane fuel, the fuel will just pre-ignite before reaching the compression stroke and that is bad for the engine.

Now Mazda claims to have developed a system which can monitor and fire the spark plugs and create a pre-ignition (which is now a part of the cycle rather than unintended) before it ignites under the full compression. Benefits include high torque and efficiency typical of high compression diesel engines, but with cleaner petrol emissions.

Sounds complex when it comes to fueling requirements and longevity of the things. My biggest doubt is how they have overcome pre-ignition and made it desirable, so to speak. Hope Mazda cracks it right.

Last edited by CrAzY dRiVeR : 10th August 2017 at 08:23.
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Old 10th August 2017, 08:52   #3
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Default re: Mazda plans a new engine using both - compression & spark ignition

Quote:
Originally Posted by hserus View Post
https://www.topgear.com/car-news/fut...bustion-engine

The engine fires using both compression (like diesels) and spark plug (like petrol mills), not sure just how they managed that.

I wonder just what fuel air mixture and compression ratio adjustment they worked out to manage this and not have the engine catch fire.

What do we have here, an engine that behaves like a diesel if you fill diesel and like a petrol if you fill petrol? One that runs on half petrol half diesel?
Mazda is on a high with their Skyactiv Petrol and Skyactiv Diesels. They are thinking outside the box and have tumbled the box upside down so that their Diesels run lower compression and Petrols run higher compression But Skyactiv Diesels have/had a problem of engine oil dilution with Diesel and the oil level in the sump rising. Their solution was to change the dipstick Anyway hope the engines are reliable.
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Old 10th August 2017, 09:04   #4
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Default re: Mazda plans a new engine using both - compression & spark ignition

This tech is very similar to what Merc and Ferrari (probably renault? not sure!) are using in F1 - Homogenous Charge Compression Ignition. A pure HCCI engine does not require spark plugs. However the ones being developed right now are still hybrids that use spark plugs. HCCI is used for cruising at low speeds while it shifts to spark plugs when under load such as when accelerating or running at high speeds.

However here they are more optimized for longevity and efficiency than outright power (though both power and efficiency are in a sense interrelated).

The primary advantage over conventional GDI engines is that the fuel burns better and with efficiencies approaching 55% in the ideal case - very similar to the efficiency of a diesel engine.

Many companies are looking at this tech for its potential benefits - VW, GM, Hyundai and now Mazda as it offers better combustion of the fuel with far less NOx emissions. The latter is essential to reach emission targets imposed by governments around the world.

Just like we saw a large scale shift from EFI naturally aspirated engines to GDI turbos in the automotive world in the last few years, the next shift would be to HCCI. Unlike downsizing though, this might offer real benefits.

Last edited by reignofchaos : 10th August 2017 at 09:12.
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Old 10th August 2017, 19:54   #5
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Default Re: Mazda plans a new engine using both - compression & spark ignition

First the Miller cycle, and now HCCI (when others seem to have given up on it).
Working with the Wankel must have really built character at Mazda.

Regards
Sutripta
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Old 12th August 2017, 11:17   #6
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Default Re: Mazda plans a new engine using both - compression & spark ignition

Quote:
Originally Posted by hserus View Post
https://www.topgear.com/car-news/fut...bustion-engine
The engine fires using both compression (like diesels) and spark plug (like petrol mills), not sure just how they managed that.
I wonder just what fuel air mixture and compression ratio adjustment they worked out to manage this and not have the engine catch fire.
What do we have here, an engine that behaves like a diesel if you fill diesel and like a petrol if you fill petrol? One that runs on half petrol half diesel?
Thanks for the update, hserus - the dividing lines between compression ignition / spark ignition is getting increasingly blurred! For one, the compression ratios are getting inverted and so are the performance characteristics - with diesels going up to 5200 rpm (http://www.mazda.com/en/innovation/t...iv/skyactiv-d/), with the gasoline engines giving comparative torque/power outputs & calorific inefficiencies, while their diesel counterparts are claiming particulate emissions comparable to their gasoline stablemates!

The best of all possible worlds indeed. For diesel addicts like me, it is music to the ears that significant engine weight reductions are in the pipeline, due to the lighter scantlings all round, including smaller crank pin/main bearing sizes - the domino effect from that reduced comp. ratio, resulting in reduced stress thresholds!

Well, alright, so there are a few hiccups too - cold start niggles and warm-up misfiring being the ones highlighted in the media releases - but where's the harm in keeping fingers crossed & hoping for the best! In this Utopian world, one can just hope that M&M and TM-JLR try to catch up as best they can!

Last edited by shashanka : 12th August 2017 at 11:24.
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Old 12th August 2017, 11:32   #7
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Default Re: Mazda plans a new engine using both - compression & spark ignition

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Originally Posted by Sutripta View Post
First the Miller cycle, and now HCCI (when others seem to have given up on it).
Working with the Wankel must have really built character at Mazda.
I still miss the Wankels. Pollution and fuel consumption killed these ultra compact and smooth mills.
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