Diesel vs Petrol Engine Technology?
Discussion
OP your wrong. Petrols have been advancing lots in the last couple of years. There is a trend for downsizing the engine capacity and sticking on a turbocharger, giving improved 'real world' performance (due to the extra torque) and much improved fuel economy. So in actual fact petrol is advancing just as fast as diesel. The latest petrol engines are just as economical as diesels from a few years ago.
VW Golf is a good example of this. The new 1.2 TSI 105 engine is faster than the 1.6 N/A petrol it replaces, and delivers fuel economy almost as good as the 1.9 TDI 105 from 5 years ago.
VW Golf is a good example of this. The new 1.2 TSI 105 engine is faster than the 1.6 N/A petrol it replaces, and delivers fuel economy almost as good as the 1.9 TDI 105 from 5 years ago.
Both petrol and diesel have come on a long way. My Z4C had 265bhp from a 3 litre straight six, running through a low ratio back axle, but despite that returned over 40mpg on the motorway! That's one hell of a petrol engine. I'd say the evolution of the two fuel types in terms of efficiency has been comparable.
Edited by RobM77 on Monday 17th January 15:36
EDLT said:
If you look at reliability then diesel engines have gone backwards.
Is it less reliabilty due to the new tech though? Meaning stuff like the 1.2 TCE renault use or the 1.4 tsi VAG lump will eventually be seen as unreliable?Oh and would reliabilty be such an issue if there weren't so many big bills associated with diesels?
Byard said:
Diesel Engine Technology seems to keep advancing, more power, better MPG etc, wheras petrol hasn't really (AFAIK) come along much? Or am I wrong?
I think there have been a number of significant changes. For example in petrol cars since the mid 80's they have mostly changed to EFI, multivalve DOHC engines, using all alloy blocks and heads.More extensive use of lightweight components and a load of tech such as variable valve control, variable timing control, variable induction length intake manifolds.
Diesel engines by and large had stuck with OHV and push rods for a long time. Although advancements such as direct injection where a huge leap. But it's only been in recent years that diesels have caught up using DOHC setups and multivalve technology.
The biggest leap has been the not so new, but new to the automotive industry of high pressure common rail direct injection. But in fairness there are also some petrol engines also using this, although less common I admit.
Everything else has been done by petrol before really.
e.g. these new compound boost and bi-turbo setups (BMW 335D for example). Take a look at the FD Mazda RX-7 and the Toyota Supra MK IV.
Petrol engines continue to develop with the Fait Twin Air, Duccati's solenoid activated valve technology (Rover had a similar concept a number of years back). And of course mass produced compound boost setups running super and turbochargers.
Then there's the whole displacement on demand technology too.
I like diesels, but in fairness I'd say a modern petrol engine is still the more complex most of the time.
Commonrail and high pressure fully electronic injection was a big leap in diesels, although the idea would have been bubbling for years, just waiting for the technology to match up.
I guess the biggest things with petrol engines over the last decade or so has been electronic throttles and torque based power control, rather than directly moving the throttle plate, Direct injection for petrols, and a special nod to BMW for their valvetronic throttleless engines, although that is more of a rethinking of how to do stuff rather than an massive new leap.
I guess the biggest things with petrol engines over the last decade or so has been electronic throttles and torque based power control, rather than directly moving the throttle plate, Direct injection for petrols, and a special nod to BMW for their valvetronic throttleless engines, although that is more of a rethinking of how to do stuff rather than an massive new leap.
The engine in my Z4 seems fairly complex. It's the N52 engine and has things like double Vanos and Valvetronic which adjust cam timing and valve lift iirc. I think it may also direct injection, although this could be the N53 I'm thinking of.
Edited by fraserbottomley on Monday 17th January 16:27
I was talking a while back with a guy who is quite well placed in the oil industry who told me that many engine manufacturers developement of diesels has hit a plateau and was slowly coming to a standstill.
how true it is I dont know.
modern diesels are superb compared to just ten years ago but they are less reliable than those from say forty years ago,they have gone massively backwards in that respect.
high pressure injection on petrol engines dont seem that reliable either.
how true it is I dont know.
modern diesels are superb compared to just ten years ago but they are less reliable than those from say forty years ago,they have gone massively backwards in that respect.
high pressure injection on petrol engines dont seem that reliable either.
Diesel and Gasoline engines are pretty much identical now, both are direct injected, turbocharged, with varriable cam timing and varriable intake geometery. Petrols have lost their thottles whilst diesels have gain them! They are both closely managed with high precision engine management systems.
The only real difference is now the Diesels slight raw fuel economy benefit (from a more optimum higher compression ratio (better thermal cycle efficiency) and the petrols power benefit (diesels slower burn rate is now the limiting power factor)
Reliability wise all the parts on the engines have got much more reliable, but unfortunately that has been somewhat offset by the shear number of parts required now (remember, the part you don't fit can't fail!). (also, the move to much much longer service intervals has reduced reliablity a bit too).
the "new frontier" is now to optimise the vehicle itself. To engineer the highest possible overall transmission ratio to downspeed the engine, reduce aero and rolling friction, to add "smart" subsystems like stopstart, smart alternators, smart aero and cooling systems etc!
Never has the car buyer bought such a complete product for his money, and a car that can do 0-60 in less that 7sec, be quiet and reffined to drive, and yet still get 50mpg would have been genuinely amazing as little as 10 years ago.
The downside, complicated things go wrong, and when they do, they are difficult and expensive to fix ;-(
The only real difference is now the Diesels slight raw fuel economy benefit (from a more optimum higher compression ratio (better thermal cycle efficiency) and the petrols power benefit (diesels slower burn rate is now the limiting power factor)
Reliability wise all the parts on the engines have got much more reliable, but unfortunately that has been somewhat offset by the shear number of parts required now (remember, the part you don't fit can't fail!). (also, the move to much much longer service intervals has reduced reliablity a bit too).
the "new frontier" is now to optimise the vehicle itself. To engineer the highest possible overall transmission ratio to downspeed the engine, reduce aero and rolling friction, to add "smart" subsystems like stopstart, smart alternators, smart aero and cooling systems etc!
Never has the car buyer bought such a complete product for his money, and a car that can do 0-60 in less that 7sec, be quiet and reffined to drive, and yet still get 50mpg would have been genuinely amazing as little as 10 years ago.
The downside, complicated things go wrong, and when they do, they are difficult and expensive to fix ;-(
Some basic common raid diesel faults are phenominally expensive to fix.
Everything from a duel mass flywheel (£1300ish on a mondeo), to injector replacement (£250 per injector on mondeo plus £200 for "electronic calibration") really kicks the idea of getting a cheap high mileage diesel in the arse.
I think if you get a good diesel engine, and it goes on forever you are a winner. Knew a guy that dealt with taxi companies a lot for his job and knew of a lot of 180,000 mile plus TDCi Mondeo cars with absolutely no problems, whereas a mate had a flywheel, injector set and 4 seperate sensors go in a year. Luckily it was a company car so he didn't have to pay.
Would similar problems in a petrol be quite so expensive? Probably not.
Everything from a duel mass flywheel (£1300ish on a mondeo), to injector replacement (£250 per injector on mondeo plus £200 for "electronic calibration") really kicks the idea of getting a cheap high mileage diesel in the arse.
I think if you get a good diesel engine, and it goes on forever you are a winner. Knew a guy that dealt with taxi companies a lot for his job and knew of a lot of 180,000 mile plus TDCi Mondeo cars with absolutely no problems, whereas a mate had a flywheel, injector set and 4 seperate sensors go in a year. Luckily it was a company car so he didn't have to pay.
Would similar problems in a petrol be quite so expensive? Probably not.
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