Discussion on Downsizing engines for emissions. - 1.0 and small ecoboost engines

Honest John Back Room » Motoring discussion
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Thu 2 Nov 2017 11:27
Discussion on Downsizing engines for emissions. - 1.0 and small ecoboost engines - oldroverboy.

www.infineuminsight.com/insight/may-2015/investiga...n

Very Very interesting reading.

Downsized engines suffer from pre-ignition

Downsized and boosted gasoline engines can operate at low speeds and high torque and have been known to exhibit disruptive abnormal combustion, such as knocking and a new phenomenon known as low-speed pre-ignition or LSPI.

LSPI occurs early in the combustion cycle and always prior to spark-triggered ignition. Its initial combustion is relatively slow and similar to normal spark initiated combustion, but then there is significantly advanced combustion timing. This can lead to very heavy knock, which can in turn cause catastrophic damage in only a few engine cycles. LSPI is especially important for pistons and connecting rods because they are rising when the aberrant combustion event occurs. In the most severe cases, LSPI can lead to broken piston rings, damaged pistons and bent connecting rods.

Reply | Report as offensive | Link
Thu 2 Nov 2017 11:36
Discussion on Downsizing engines for emissions. - 1.0 and small ecoboost engines - craig-pd130

It is interesting, especially this bit: "When the fuel is injected directly into the combustion chamber, it dilutes the oil film lining the cylinder. This fuel dilution reduces the surface tension and viscosity of the oil, causing an oil-fuel mixture to accumulate in the upper reaches of the piston top land crevice. The mechanical energy of the upstroke during compression pushes droplets into the combustion chamber, where they vaporise and can auto-ignite prior to spark ignition."

To me, this implies it's a combination of direct injection (i.e. not 'conventional' throttle-body injection) and a high CR causing 'dieseling'

Reply | Report as offensive | Link
Thu 2 Nov 2017 13:27
Discussion on Downsizing engines for emissions. - 1.0 and small ecoboost engines - Engineer Andy

It is interesting, especially this bit: "When the fuel is injected directly into the combustion chamber, it dilutes the oil film lining the cylinder. This fuel dilution reduces the surface tension and viscosity of the oil, causing an oil-fuel mixture to accumulate in the upper reaches of the piston top land crevice. The mechanical energy of the upstroke during compression pushes droplets into the combustion chamber, where they vaporise and can auto-ignite prior to spark ignition."

To me, this implies it's a combination of direct injection (i.e. not 'conventional' throttle-body injection) and a high CR causing 'dieseling'

It'll be inetersting to see how Mazda's much vaunted HCCI engines fare when they arrive on the scene in 2019, given they are effectively using diesel technology in a petrol engine. Mazda need to be REALLY careful here, as they have currently, in my view, got a customer perception problem with their diesel engine reliability, and if that expands to their petrol engine range, then that could mean REALLY BAD porblems from them, given they are no longer jointly owned by Ford and as such don't have the finanical clout to withstand a VAG style PR nightmare.

Many YouTube videos regularly show how poor a state many DI petrol cars valves are compared to 'old style FI' ones after 30-50k miles, and the problems that result, plus the need for them to be either replaced or cleaned, both of which are not cheap.

It seems the tech is reducing costs in terms of better mpg (for a while) but then loading far more up as parts wear out quicker (apparently this issue also reduces mpg when it gets bad) due to (IMO) inherrant design flaws in the concept of DI petrol engines. You have to wonder if the manufacturers are doing this deliberately to get more post-sales custom.

Reply | Report as offensive | Link
Thu 2 Nov 2017 13:38
Discussion on Downsizing engines for emissions. - 1.0 and small ecoboost engines - Metropolis.
No replacement for displacement!
Reply | Report as offensive | Link
Thu 2 Nov 2017 14:07
Discussion on Downsizing engines for emissions. - 1.0 and small ecoboost engines - focussed

Downsized engines suffer from being far too small to do the job they are supposed to do properly and in the long term.

I remember laughing long and loud when Ford were crowing about how their ecoboost lawn mower engine's block footprint would fit on a sheet of A4 paper!

Reply | Report as offensive | Link