Why are hybrids petrol engined?
Discussion
Latest Car Magazine carries a story about a new 5 Series hybrid petrol/electric and concludes (as ever) that the diesel 5 Series would be quicker, cheaper, and crucially, more economical.
So surely the obvious thing to so is start off with the most economical diesel and then use technology to improve it, rather than using technology to improve a less efficient model to the point where it's still not quite as good as the diesel?
At the moment I can see zero reason for anyone to buy the hybrid 5 Series over the diesel.
So surely the obvious thing to so is start off with the most economical diesel and then use technology to improve it, rather than using technology to improve a less efficient model to the point where it's still not quite as good as the diesel?
At the moment I can see zero reason for anyone to buy the hybrid 5 Series over the diesel.
Peugeot do hybrid diesel, and some others are planning them.
The thing with diesels is that the only metric they're good at is low CO2 figures. Pretty much every other air quality metric (NOx, SO2, particulates, etc) favours petrol over diesel, and these are the ones that have the most impact on health - hence schemes like the Low Emission Zone for users of commercial diesel vehicles in London. Given that hybrids will tend to be used by city-dwellers, they'd be even more prone to the DPF issues that many modern diesels have.
The petrol engines in most hybrids are Atkinson cycle rather than conventional Otto cycle and would be very efficient without all the hybrid gubbins. They'd be very flat to drive though, so the battery and motors help a lot to make the cars feel more responsive.
The thing with diesels is that the only metric they're good at is low CO2 figures. Pretty much every other air quality metric (NOx, SO2, particulates, etc) favours petrol over diesel, and these are the ones that have the most impact on health - hence schemes like the Low Emission Zone for users of commercial diesel vehicles in London. Given that hybrids will tend to be used by city-dwellers, they'd be even more prone to the DPF issues that many modern diesels have.
The petrol engines in most hybrids are Atkinson cycle rather than conventional Otto cycle and would be very efficient without all the hybrid gubbins. They'd be very flat to drive though, so the battery and motors help a lot to make the cars feel more responsive.
sjg said:
Peugeot do hybrid diesel, and some others are planning them.
The thing with diesels is that the only metric they're good at is low CO2 figures. Pretty much every other air quality metric (NOx, SO2, particulates, etc) favours petrol over diesel, and these are the ones that have the most impact on health - hence schemes like the Low Emission Zone for users of commercial diesel vehicles in London. Given that hybrids will tend to be used by city-dwellers, they'd be even more prone to the DPF issues that many modern diesels have.
The petrol engines in most hybrids are Atkinson cycle rather than conventional Otto cycle and would be very efficient without all the hybrid gubbins. They'd be very flat to drive though, so the battery and motors help a lot to make the cars feel more responsive.
According to the Wiki its not the proper Atkinson cycle where the cycle did all 4 "strokes" in one rotation of the crank, and had a odd crank design that allowed a longer expansion stroke than the compression stroke (more work out for given work in). The modern take is a modified Otto cycle with a valve timing arrangement that mimicked the unequal compression and expansion ratios.The thing with diesels is that the only metric they're good at is low CO2 figures. Pretty much every other air quality metric (NOx, SO2, particulates, etc) favours petrol over diesel, and these are the ones that have the most impact on health - hence schemes like the Low Emission Zone for users of commercial diesel vehicles in London. Given that hybrids will tend to be used by city-dwellers, they'd be even more prone to the DPF issues that many modern diesels have.
The petrol engines in most hybrids are Atkinson cycle rather than conventional Otto cycle and would be very efficient without all the hybrid gubbins. They'd be very flat to drive though, so the battery and motors help a lot to make the cars feel more responsive.
I think my Honda is probably part atkinson cycle. At <50% throttle or <3500rpm the intake valves stay open for part of the compression stroke to essentially throttle the engine. The throttle valve is left WO, and the mixture is just pushed out by the piston instead until the required amount is there. Basically shortens your compression ratio at part load and eliminates throttle losses. Doesnt seem to do much though! 42mpg is the best i've had of it on a run. Suppose its alright for a 1.8 N/A engine.
Yes it is very flat when its in that eco-mode!
Diesel engines are very very expensive to produce.
The common rail technology, the fuel system and all the control systems, ensure that they're much more expensive to produce than say, a BMW 'M' engine.
The problem is worse on smaller 'white goods' cars where there are smaller profit margins.
A good compromise may be a diesel with stop-start Integrated starter generator or Belt-alternator-starter
The common rail technology, the fuel system and all the control systems, ensure that they're much more expensive to produce than say, a BMW 'M' engine.
The problem is worse on smaller 'white goods' cars where there are smaller profit margins.
A good compromise may be a diesel with stop-start Integrated starter generator or Belt-alternator-starter
I seem to recall it's a technical issue of mating an engine with the torque characteristics of a diesel, to an electric motor. Can't remember the details of the explanation, or where I read it, but that was the answer. Peugeot have spent a v.long time trying to make it happen, but that's because the taxation system in non-oil producing European countries favours diesel, so only a diesel hybrid would really make financial sense to the punter. In Japan, the economic argument doesn't stack up, as they favour air quality over fuel economy, and tax petrol/diesel accordingly.
agentsmith said:
yes but AFAIK you dont get stop/start with bmw diesels (of which you have to do a lot of in USA) with the AIR CON on. I believe the system in the Prius and Camry hybrids are electric...?
Yes you do, and IIRC they were the first to do it.Edit: Missed your Air Con bit
. They still do, it just depends on the power required to run the aircon/heater/heated seats etc.Edited by onesickpuppy on Tuesday 28th February 14:51
t and you can't filter out the worst of it. A lot of the issue is the CVT gearbox which youll find in a full hybrid. Such as the Prius/Auris/Yaris Hybrids, it wouldnt handle the torque a diesel puts through it, so therefore petrol works better.
The Honda hybrid system isnt anything like the Toyota system, hence they wouldnt have a problem. They have an electrically assited petrol engine, the Toyota is a Electric Motor assisted by a petrol motor.
The diesel version Peugeot have, believe it of not, doesnt go through the normal gearbox. Only powers the rear wheels, and the diesel does the job at the front powering the front wheels.
The Honda hybrid system isnt anything like the Toyota system, hence they wouldnt have a problem. They have an electrically assited petrol engine, the Toyota is a Electric Motor assisted by a petrol motor.
The diesel version Peugeot have, believe it of not, doesnt go through the normal gearbox. Only powers the rear wheels, and the diesel does the job at the front powering the front wheels.
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