Petrol engines in EVs - warming up
Discussion
As petrol heads we all know that when you start driving your car you should let the engine 'warm up' before giving it the beans to reduce engine wear.
How does this work with hybrid cars? Say I go for a drive in my new BMW i8 (I wish). First part of the drive is through town, lots of stop/start traffic, running purely on electric power. I then hit a stretch of B road and want to dirve in a more spirited manner. My petrol engine then spins into life, but do I then need to let it warm up for 10 minutes before flooring it?
With the engine activating, de-activating intermittently, depending on driving conditions, will your engine be getting thrashed from cold all the time?
Just wondering, that's all!
How does this work with hybrid cars? Say I go for a drive in my new BMW i8 (I wish). First part of the drive is through town, lots of stop/start traffic, running purely on electric power. I then hit a stretch of B road and want to dirve in a more spirited manner. My petrol engine then spins into life, but do I then need to let it warm up for 10 minutes before flooring it?
With the engine activating, de-activating intermittently, depending on driving conditions, will your engine be getting thrashed from cold all the time?
Just wondering, that's all!
CaptainSensib1e said:
As petrol heads we all know that when you start driving your car you should let the engine 'warm up' before giving it the beans to reduce engine wear.
How does this work with hybrid cars? Say I go for a drive in my new BMW i8 (I wish). First part of the drive is through town, lots of stop/start traffic, running purely on electric power. I then hit a stretch of B road and want to dirve in a more spirited manner. My petrol engine then spins into life, but do I then need to let it warm up for 10 minutes before flooring it?
With the engine activating, de-activating intermittently, depending on driving conditions, will your engine be getting thrashed from cold all the time?
Just wondering, that's all!
A couple of techniques are used:How does this work with hybrid cars? Say I go for a drive in my new BMW i8 (I wish). First part of the drive is through town, lots of stop/start traffic, running purely on electric power. I then hit a stretch of B road and want to dirve in a more spirited manner. My petrol engine then spins into life, but do I then need to let it warm up for 10 minutes before flooring it?
With the engine activating, de-activating intermittently, depending on driving conditions, will your engine be getting thrashed from cold all the time?
Just wondering, that's all!
1) High loads and speeds are not necessarily bad for an engine designed to run under those conditions. ie, a conventional engine makes peak power up at say 6500rpm, but you drive it at around 2k most of the time, and it has piston/bore clearances optimised for fully warm operation. Range extenders can be optimised to operate when cold (generally with the effect of being a bit noiser due to the necessary larger clearances).
2) The engine coolant is often "prewarmed" by the hybrid cooling system. IE heat from the battery, inverter and motor used to warm up the ice engine even when it is not actually running
3) The engine may be started and warmed fully before it is shut down again, rather than just being turned on and off for short periods to minimise wear etc.
4) In the real world, with the battery system providing significant performance on it's own, the engine is not actually required to start and immediately go to full power when cold (and often not even when warm)
5) From a "tailpipe" emissions & economy point of view, starting and running at a high(ish) load reduces both as the engine warms up quicker, compared to starting and idling or driving at low speed / load
Speaking from the Hybrid viewpoint of the Prius (and I have had two).
Whenever the ICE fires up it will run through a catalyst warm up cycle to reduce emissions. Once warm it will kick in and out as required. Having such a small traction battery, its on most of the time by design though.
There is a common fault with the Prius and Lexus ICE in so far as if the engine begins its warm up cycle and you switch off (ie your moving the car off the drive to get to something else and you neglect to put it into EV mode) before the warm up has completed. On restart, the next day, if its been damp overnight, the build up of condensation in the air intake makes it sound like a bag of spanners.
see:
https://www.youtube.com/watch?v=OiVAblf4xAM
Regarding range extender EV's on my test drive of an Ampera I believe the engine does go through a cold start warm up to lower emissions also.
Not sure about a i3 and i8 or Outlander.
Whenever the ICE fires up it will run through a catalyst warm up cycle to reduce emissions. Once warm it will kick in and out as required. Having such a small traction battery, its on most of the time by design though.
There is a common fault with the Prius and Lexus ICE in so far as if the engine begins its warm up cycle and you switch off (ie your moving the car off the drive to get to something else and you neglect to put it into EV mode) before the warm up has completed. On restart, the next day, if its been damp overnight, the build up of condensation in the air intake makes it sound like a bag of spanners.
see:
https://www.youtube.com/watch?v=OiVAblf4xAM
Regarding range extender EV's on my test drive of an Ampera I believe the engine does go through a cold start warm up to lower emissions also.
Not sure about a i3 and i8 or Outlander.
Modern oils help, there's no doubt about that! But the issue is one of piston to bore clearance. This must be as tight as possible to minimise mechanical noise, reduce friction, and crucially these days to reduce emissions (to minimise crevice volumes and oil carry over).
Because the piston itself has a much lower thermal mass that the engine block, if you drive your car hard from cold, the piston warms up before the block does, and as a result expands faster than the bore. This reduces that critical bore clearance and deforms the carefully chosen piston profiles (pistons are "barrel shaped btw, and often not round either!). Carefully formulated and chosen materials can minimise the expansion co-efficient of the piston but nothing can eliminate this factor entirely.
As the bore to piston interface is optimised for a "warm" engine, running under high loads with a cold engine can lead to a more rapid rate of wear. These days, modern oils, and special low friction coatings on the pistons generally prevent immediate catastrophic failures under these conditions (oil film reduced to zero = hot spot = ring/skirt damage = pre ignition = dead engine!)
Pretty much the rest of the engine doesn't really care to much about it's temperature, as there is generally a much more even temp gradient (bearings, cam drive etc) and things like the valvetrain actually prefer going "fast" to going slow when cold (cam lobe/lifter scuffing etc)
Because the piston itself has a much lower thermal mass that the engine block, if you drive your car hard from cold, the piston warms up before the block does, and as a result expands faster than the bore. This reduces that critical bore clearance and deforms the carefully chosen piston profiles (pistons are "barrel shaped btw, and often not round either!). Carefully formulated and chosen materials can minimise the expansion co-efficient of the piston but nothing can eliminate this factor entirely.
As the bore to piston interface is optimised for a "warm" engine, running under high loads with a cold engine can lead to a more rapid rate of wear. These days, modern oils, and special low friction coatings on the pistons generally prevent immediate catastrophic failures under these conditions (oil film reduced to zero = hot spot = ring/skirt damage = pre ignition = dead engine!)
Pretty much the rest of the engine doesn't really care to much about it's temperature, as there is generally a much more even temp gradient (bearings, cam drive etc) and things like the valvetrain actually prefer going "fast" to going slow when cold (cam lobe/lifter scuffing etc)
Max_Torque said:
Modern oils help, there's no doubt about that! But the issue is one of piston to bore clearance. This must be as tight as possible to minimise mechanical noise, reduce friction, and crucially these days to reduce emissions (to minimise crevice volumes and oil carry over).
Because the piston itself has a much lower thermal mass that the engine block, if you drive your car hard from cold, the piston warms up before the block does, and as a result expands faster than the bore. This reduces that critical bore clearance and deforms the carefully chosen piston profiles (pistons are "barrel shaped btw, and often not round either!). Carefully formulated and chosen materials can minimise the expansion co-efficient of the piston but nothing can eliminate this factor entirely.
As the bore to piston interface is optimised for a "warm" engine, running under high loads with a cold engine can lead to a more rapid rate of wear. These days, modern oils, and special low friction coatings on the pistons generally prevent immediate catastrophic failures under these conditions (oil film reduced to zero = hot spot = ring/skirt damage = pre ignition = dead engine!)
Pretty much the rest of the engine doesn't really care to much about it's temperature, as there is generally a much more even temp gradient (bearings, cam drive etc) and things like the valvetrain actually prefer going "fast" to going slow when cold (cam lobe/lifter scuffing etc)
I knew someone clever would be along to explain it Because the piston itself has a much lower thermal mass that the engine block, if you drive your car hard from cold, the piston warms up before the block does, and as a result expands faster than the bore. This reduces that critical bore clearance and deforms the carefully chosen piston profiles (pistons are "barrel shaped btw, and often not round either!). Carefully formulated and chosen materials can minimise the expansion co-efficient of the piston but nothing can eliminate this factor entirely.
As the bore to piston interface is optimised for a "warm" engine, running under high loads with a cold engine can lead to a more rapid rate of wear. These days, modern oils, and special low friction coatings on the pistons generally prevent immediate catastrophic failures under these conditions (oil film reduced to zero = hot spot = ring/skirt damage = pre ignition = dead engine!)
Pretty much the rest of the engine doesn't really care to much about it's temperature, as there is generally a much more even temp gradient (bearings, cam drive etc) and things like the valvetrain actually prefer going "fast" to going slow when cold (cam lobe/lifter scuffing etc)
ORD said:
Max_Torque said:
Modern oils help, there's no doubt about that! But the issue is one of piston to bore clearance. This must be as tight as possible to minimise mechanical noise, reduce friction, and crucially these days to reduce emissions (to minimise crevice volumes and oil carry over).
Because the piston itself has a much lower thermal mass that the engine block, if you drive your car hard from cold, the piston warms up before the block does, and as a result expands faster than the bore. This reduces that critical bore clearance and deforms the carefully chosen piston profiles (pistons are "barrel shaped btw, and often not round either!). Carefully formulated and chosen materials can minimise the expansion co-efficient of the piston but nothing can eliminate this factor entirely.
As the bore to piston interface is optimised for a "warm" engine, running under high loads with a cold engine can lead to a more rapid rate of wear. These days, modern oils, and special low friction coatings on the pistons generally prevent immediate catastrophic failures under these conditions (oil film reduced to zero = hot spot = ring/skirt damage = pre ignition = dead engine!)
Pretty much the rest of the engine doesn't really care to much about it's temperature, as there is generally a much more even temp gradient (bearings, cam drive etc) and things like the valvetrain actually prefer going "fast" to going slow when cold (cam lobe/lifter scuffing etc)
I knew someone clever would be along to explain it Because the piston itself has a much lower thermal mass that the engine block, if you drive your car hard from cold, the piston warms up before the block does, and as a result expands faster than the bore. This reduces that critical bore clearance and deforms the carefully chosen piston profiles (pistons are "barrel shaped btw, and often not round either!). Carefully formulated and chosen materials can minimise the expansion co-efficient of the piston but nothing can eliminate this factor entirely.
As the bore to piston interface is optimised for a "warm" engine, running under high loads with a cold engine can lead to a more rapid rate of wear. These days, modern oils, and special low friction coatings on the pistons generally prevent immediate catastrophic failures under these conditions (oil film reduced to zero = hot spot = ring/skirt damage = pre ignition = dead engine!)
Pretty much the rest of the engine doesn't really care to much about it's temperature, as there is generally a much more even temp gradient (bearings, cam drive etc) and things like the valvetrain actually prefer going "fast" to going slow when cold (cam lobe/lifter scuffing etc)
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