Jul. 22nd, 2016

cabcat: (pleasant)
On the new FA20F engine in the WRX it is in layman’s terms an 86/BRZ engine turboed with a twin scroll turbo charger and using Subaru's direct injection system rather than Toyota's D4-S found on the 86/BRZ.  Subaru's system uses an inbuilt air/oil separator to reduce/stop the build-up of carbon deposits on the backs of the intake valves a process some of you older mechanics and car guys will know as "coking".  It even has a separate oil pump for the catcher unit in the separator.  Toyota's D4-S system uses a combination of port and direct injection to keep valves clean.  For more details on the FA20F see here: http://australiancar.reviews/Subaru_FA20E-FA20F_Engines.php

I looked into this engine because I was researching a bit on DI engines and their intake valve deposit issues that were apparent on earlier vehicles and particularly bad on some.  When it got bad the engine would often run rough and throw fault codes usually requiring removal of the heads and decarbonising or walnut shell blasting with the heads still attached, not a cheap process.  This is an issue which hadn't been encountered on port fuel injection engines or carb engines with PCV and EGR systems since the advent of detergent fuels.

For those that don't know since direct injection sprays directly into the combustion chamber the detergent fuels were no longer washing over the back of the intake valves.  This allowed oil fumes from PCV and EGR systems to land on the back of the intake valves and bake on.  Normally in port injection the fuel washing over the back of the intake valves would keep them clean or help to keep them clean, with that gone the carbon deposits would build up and eventually effect the air intake and valve sealing around the area.

The problem became apparent on many of the early adopters of direct injection with VW, Audi, BMW and more all reporting issues.  It wasn't just the European marques that were affected, Lexus engines that used only DI like the 2.5L V6 4GR-FSE found in the IS250 also suffered from issues.  The Lexus 3.5L V6 2GR-FSE found in the Lexus IS350 was immune as it used the D4-S system using a combination of direct and port fuel injection.  Ford also had issues with the DI ecoboost engines early on which was also a problem if you tried to run an induction cleaner through the intake as it often caused Turbo failures due to overheating.  As described by a Ford tech here. 
Part 1    Part 2.   Ways to reduce the problem were to aid an aftermarket air/oil separator, oil catch cans and running the car at higher revs for a time to burn off deposits.  A bit like how you burn out diesel particulate filters.  Sometimes known colloquially as "the Italian tune up" probably because of the issues you'd get if you drove a Ferrari or Maserati at dawdling speeds all the time, often a highway burn would fix the issue.

So what are doing or have done:

  • Toyota will probably use the D4-S system on all DI engines since it works or a variation of it like the ESTEC D4-ST found on the 2.0L 4cylinder turbo 8AR-FTS found in Lexus 200t models. 

  • Mazda, in their Skyactive-G engines, designed the head so the heat pathways keep the intake valves hotter.  I think this was so the oil fumes would flash burn rather than land and bake onto the valve.

  • Subaru have incorporated a factory air/oil separator with a separate scavenger pump.

  • Ford use some kind of cam phasing and timing create a different EGR environment.

  • I think Honda and Hyundai use a different kind of PCV and EGR system.

  • I'm not sure what the European marques are doing but I'd image they're doing similar things.

So it's not like makers are not sitting on their laurels, we are however I think reaching the limits of efficiency with the internal combustion engine.  I've come across engines which I didn't realise run a combination of the Otto cycle and the Atkinson cycle which from an engineering point of view is amazing :).

The other thing worth looking into if you’re interested in the new direct injection setup is Toyota’s D4-S, here is a quote from the engine site I listed earlier in regards to why you would want to run a mixture of port and direct fuel injection.

Generally, direct injection lowers the tendency to knock such that they can operate at higher compression ratios and increases performance by reducing the charge intake temperature. At low engine speeds and high loads, however, direct injection is inferior to port injection in forming a homogeneous air-fuel mixture where there is little time to form a homogeneous mixture – from the time fuel is injected until ignition occurs – due to mixture stratification in the combustion chamber. To overcome this problem and produce a homogeneous air-fuel mixture, direct injection engines generally use devices such as:

  • A tumble intake-port;

  • A helical intake-port; or,

  • A swirl control valve.

These mechanisms, however, decrease intake-port flow efficiency relative to a port-injected engine and inhibit performance at high engine speeds. The D4-S system switches to the port injectors to achieve mixture formation in these conditions without the need for swirl ports or different piston crown shapes.”

There endeth the lessoneth.
And now Stubby Bob in Roadkill

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