Mild hybrids - what am I missing?
Discussion
So, many new cars at the moment seem to employ mild hybrid systems that pair a small turbo charged petrol engine with a small electric motor to provide improved fuel economy.
They also seem to have ditched offering diesel engines, which on paper at least are far more fuel efficient. Take the Nissan Quashqai, the old 1.5 diesel had combined fuel consumption of 67.2 mpg. The new 1.3 mild hybrid petrol has combined fuel consumption of 44.7mpg.
What am I missing here? Why are manufacturers developing more complicated power trains that are less fuel efficient that previous ones?
They also seem to have ditched offering diesel engines, which on paper at least are far more fuel efficient. Take the Nissan Quashqai, the old 1.5 diesel had combined fuel consumption of 67.2 mpg. The new 1.3 mild hybrid petrol has combined fuel consumption of 44.7mpg.
What am I missing here? Why are manufacturers developing more complicated power trains that are less fuel efficient that previous ones?
CaptainSensib1e said:
So, many new cars at the moment seem to employ mild hybrid systems that pair a small turbo charged petrol engine with a small electric motor to provide improved fuel economy.
They also seem to have ditched offering diesel engines, which on paper at least are far more fuel efficient. Take the Nissan Quashqai, the old 1.5 diesel had combined fuel consumption of 67.2 mpg. The new 1.3 mild hybrid petrol has combined fuel consumption of 44.7mpg.
What am I missing here? Why are manufacturers developing more complicated power trains that are less fuel efficient that previous ones?
My D300 Defender is a mild hybrid diesel.They also seem to have ditched offering diesel engines, which on paper at least are far more fuel efficient. Take the Nissan Quashqai, the old 1.5 diesel had combined fuel consumption of 67.2 mpg. The new 1.3 mild hybrid petrol has combined fuel consumption of 44.7mpg.
What am I missing here? Why are manufacturers developing more complicated power trains that are less fuel efficient that previous ones?
Pretty efficient for its size and plenty of power.
I know someone who has just bought a Suzuki Ignis very mild hybrid. It's something like a 1.5 bhp equivalent electric motor which runs off an almost standard car battery.
Suzuki's explanation for this is that it gives it enough of a boost of torque to increase the traction considerably when things get a bit slippy.
The sceptic in me thinks it might be a way to circumnavigate ULEZ type rules?
Suzuki's explanation for this is that it gives it enough of a boost of torque to increase the traction considerably when things get a bit slippy.
The sceptic in me thinks it might be a way to circumnavigate ULEZ type rules?
CaptainSensib1e said:
Pollution? By what measure? Going back to my Quashqai example:
Old diesel is 122g/km of CO2
New petrol 143g/km of CO2
CO2 isn’t a pollutant. Old diesel is 122g/km of CO2
New petrol 143g/km of CO2
Criteria emissions for the regulations are CO, NOx and PN (we do measure THCs, Methane, N2O and ammonia as well). CO2 can be as high as you like so long as you have customers who will pay the taxes. The others have not to exceed limits.
As long as the SCR and DPF systems are working properly, modern diesels are well within the limits on real world road tests. But petrols are equally as good, and they only need to fit a three way catalyst (ok and now a GPF) instead of a little chemical factory that costs more than the rest of the engine.
Megaflow said:
CaptainSensib1e said:
Pollution? By what measure? Going back to my Quashqai example:
Old diesel is 122g/km of CO2
New petrol 143g/km of CO2
NOx will be significantly higher with the diesel and is far nastier to people in the local environment Old diesel is 122g/km of CO2
New petrol 143g/km of CO2
And the reason they bought into that was because the European manufacturers lobbied the EU to give diesels preferential treatment because they had the technology and the Japanese and Americans didn't which would let them clean up in Europe. So because the government *ONLY* focused on CO2 diesels became the only option unless you wanted to pay much more.
Turned out that all the claimed improvements from the last 20+ years of NOx improvements were b
ks outside the "lab" test hence why all the tests have moved to more real world etc etc and diesels are both massively more complicated (and so more expensive) to actually hit the required NOx levels, use more fuel and with the push for EV no longer the "darling" for business. [1] Yes, yes, I know that it doesn't take that much to kill you and causes all sorts of issues with relatively low amounts but NOx is far worse.
Alex Z said:
CaptainSensib1e said:
Pollution? By what measure? Going back to my Quashqai example:
Old diesel is 122g/km of CO2
New petrol 143g/km of CO2
NOx and particulates will be far worse on the dieselOld diesel is 122g/km of CO2
New petrol 143g/km of CO2
But the cost of complying to those standards means the affordable diesel has been almost removed from the market.
And fleet sales have plummeted too.
My A3 is a MHEV. Only real thing I notice is that fact it switches the engine off and coasts in some no-load conditions, such as descending an incline, and the fact that the stop/start system is completely instantaneous and unobtrusive.
It's remarkably economical for a 150bhp petrol engine - I've not had a tank under 52mpg yet and I average high 50s/low 60s on most tanks without any real special effort (measured from brim to brim rather than OBC)
For some fairly tedious and unintended reasons, my wife currently has an identical one other than the fact it's the 2.0 (non-MHEV)diesel, and to be honest there's only 4-5mpg difference in real world conditions.
It's remarkably economical for a 150bhp petrol engine - I've not had a tank under 52mpg yet and I average high 50s/low 60s on most tanks without any real special effort (measured from brim to brim rather than OBC)
For some fairly tedious and unintended reasons, my wife currently has an identical one other than the fact it's the 2.0 (non-MHEV)diesel, and to be honest there's only 4-5mpg difference in real world conditions.
legless said:
My A3 is a MHEV. Only real thing I notice is that fact it switches the engine off and coasts in some no-load conditions, such as descending an incline, and the fact that the stop/start system is completely instantaneous and unobtrusive.
It's remarkably economical for a 150bhp petrol engine - I've not had a tank under 52mpg yet and I average high 50s/low 60s on most tanks without any real special effort (measured from brim to brim rather than OBC)
For some fairly tedious and unintended reasons, my wife currently has an identical one other than the fact it's the 2.0 (non-MHEV)diesel, and to be honest there's only 4-5mpg difference in real world conditions.
Just out of interest Legless, which one offers the better MPG?It's remarkably economical for a 150bhp petrol engine - I've not had a tank under 52mpg yet and I average high 50s/low 60s on most tanks without any real special effort (measured from brim to brim rather than OBC)
For some fairly tedious and unintended reasons, my wife currently has an identical one other than the fact it's the 2.0 (non-MHEV)diesel, and to be honest there's only 4-5mpg difference in real world conditions.
Foss62 said:
In addition, plug-in hybrids seem to get a bad press even though they allow for totally electric local journeys which seems quite a big benefit.
They would if anyone actually plugged them in; but they don't, so they aren't.The only reason for their existence are the emission rules and the tax system - that they don't actually deliver the claimed benefits is irrelevant.
Mild hybrid is really just enhanced stop/start. It can stop the engine earlier (like when you're still slowing down to a junction) and it can give a little boost when you accelerate again, but it can't move the car on electric - it's only a 48v system. They're fairly cheap, simple, light, easy to package/integrate and give a couple of g/km CO2 reduction which helps for fleet averages. With a cynical hat on, it's also a way to hoodwink the public who assume it's much greener or will save them loads of fuel.
Proper hybrids like the Toyotas can at least creep along in a traffic jam without using the engine and there's a much larger battery to buffer regen braking and use it later. They get great mpg because the Atkinson cycle engines they use are very efficient but would feel flat as a pancake without a substantial electric boost.
As others have said, getting diesels through modern emissions standards needs expensive pollution control measures. Diesels were only good at lowering CO2, at the expense of worse performance on the air quality metrics. Petrols do much better, albeit at higher CO2. Japan realised this over 20 years ago, put measures in place in cities to improve air quality and pretty much killed off diesel sales in the domestic market.
Proper hybrids like the Toyotas can at least creep along in a traffic jam without using the engine and there's a much larger battery to buffer regen braking and use it later. They get great mpg because the Atkinson cycle engines they use are very efficient but would feel flat as a pancake without a substantial electric boost.
As others have said, getting diesels through modern emissions standards needs expensive pollution control measures. Diesels were only good at lowering CO2, at the expense of worse performance on the air quality metrics. Petrols do much better, albeit at higher CO2. Japan realised this over 20 years ago, put measures in place in cities to improve air quality and pretty much killed off diesel sales in the domestic market.
Otispunkmeyer said:
CaptainSensib1e said:
Pollution? By what measure? Going back to my Quashqai example:
Old diesel is 122g/km of CO2
New petrol 143g/km of CO2
CO2 isn’t a pollutant. Old diesel is 122g/km of CO2
New petrol 143g/km of CO2
Criteria emissions for the regulations are CO, NOx and PN (we do measure THCs, Methane, N2O and ammonia as well). CO2 can be as high as you like so long as you have customers who will pay the taxes. The others have not to exceed limits.
As long as the SCR and DPF systems are working properly, modern diesels are well within the limits on real world road tests. But petrols are equally as good, and they only need to fit a three way catalyst (ok and now a GPF) instead of a little chemical factory that costs more than the rest of the engine.
CO2 is directly linked with fuel usage. It's a necessary combustion product and can't be turned in to anything else. The others can be captured/mitigated.
On MHEVs, the primary usages are:
1) Load shifting - if the engine is operating in a non-efficient regime (for BSFC), it can load the engine, and take that otherwise wasted fuel and use that for propulsive energy at other times
2) Enhanced stop-start - particularly rolling stop start. It operates so quickly that it's imperceptible to the customer (tested myself and it's true); this enables rolling stop-start and other features
3) Transient torque fill - what it says on the tin
4) Regen braking - recover otherwise completely wasted heat from braking
MHEV saves between 8-10% CO2. For the cost of the system (and the ~20-30kg weight) it's worth it.
Edited by GroundEffect on Friday 23 September 09:59
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