I sympathize with Madman, having been woken up countless times by the rod-rattler near my house.
Torque is what today's diesel owners are buying them for... my dad had a 1.9 A4 Tdi Quattro Sport... and that had the same amount of torque, i believe, as a Boxster S! The only problem is the need to change gear so quickly because of the low RPM
Would actually like to see an VW Passat like car in LFS, station wagon, or what its called.
What a Great Idear
I think its a Brill Idear,
It Means a Diff Driving Style a Diffrent Pit Option and could Make Some Hugly Good Racing,
Instead of Hitting 8K and Changing Gear its a lot Less,
Short Changing and Using the TQ instead of Just Waiting for the Littel Red Light,
Would Love to See a Diesel in LFS,
Would Make For Some Nice Throtel Controle when the TQ kicks In if a RWD,
It Means a Diff Driving Style a Diffrent Pit Option and could Make Some Hugly Good Racing,
Instead of Hitting 8K and Changing Gear its a lot Less,
Short Changing and Using the TQ instead of Just Waiting for the Littel Red Light,
Would Love to See a Diesel in LFS,
Would Make For Some Nice Throtel Controle when the TQ kicks In if a RWD,
yes.
put a small turbo in the 220 ST mondeo (or in a 2.0 mondeo - petrol engine).
easily smash the diesel version.
petrol have a better thermal efficiency.
i don't remember the exact percentage but i think is double of the thermal efficiency of a diesel engine.
the only good thing of a diesel engine is the consumption...lower diesel quantity for the same mileage...and the diesel is a little bit cheaper (in italy about 1,10 euro - petrol is 1,35 euro)...
but for sporty cars,diesel is not the better choice...
(audi R10 diesel is helped by the LMP's championship rules)
my 2 cents
(ps:sorry for my bad english!)
Me too... Real cars always make you feel good!! That's why i like PGR 3 so much!!
I agree, diesel cars are nearly always turbocharged and some have high pressure turbochargers with intercoolers. Also diesel engies have often very sophisticated injection systems to make a diesel go like a petrol...
People should compare such diesel engines with a simular sized petrol engine. the diesel will loose always and will always loose of a simular sized petrol engine with a simular good injection system and turbo charger.
For comparison, a certain real world car has a petrol 1.9 16v liter engine with a low pressure turbo. On paper it has less horsepower and torgue then many modern 1.9 tdi engines. Guess what, the easy to build, durable and reliable petrol car beats them all! Only bigger cars with diesel engines or very high pressure turbo chargers maybe faster. But those diesels use a lot of fuel too!
The torgue all those diesel drivers are talking about:
An petrol engine with direct petrol injection has an identical torgue curve as a diesel car(with or without turbo charger). But the petrol engine will keep going over 5000rpm and wins in the end. Its not the fuel that gives diesel engines the torgue, its the direct fuel injection, the bigger engine displacement(on average) and the turbochargers!
So in the end, please NO to diesel cars into lfs, diesel is not for racing but for fuel economy and sometimes safety. Well thats my opinion.
Firstly, the bit about diesels being twice as thermally efficient as a petrol engine is rubbish.
Thermal Efficiency = (Power x 2) / (bsfc * rev/second), and a diesel will often get higher, but not necessarily.
The sohpisticated diesel injection systems do not 'make it go like a petrol engine', it is primarly a NOx and Knock resistance matter, though of course it helps performance over indirect injection.
However, you are right in saying that similar sized/specced petrol and diesels will almost certainly allow the petrol to win in a straight fight (assuming sensible gearing for both cars). However, as diesels routinely run with a compression ratio of 20:1 or more they can't rev as highly (as the piston and conrod as to be stronger, and thus heavier), which severely limits a diesel in outright performance.
The MAIN advantage with diesel engines is the fact that a diesel isn't throttled. This means there is less low pressure inlet manifold air to perform work on the piston (known as pumping losses) whilst at part load. This, in turn, means that the diesel ends up more fuel conversion efficiency at part load.
For a given compression ratio the diesel actually has a much lower thermal efficiency compared to gasoline, but thermal efficiency increases with compression ratio -> it turns out that a gasoline engine at about 9:1 has the same nu_t as a diesel at 20:1 (very rough figures). Diesel combustion may be roughly simplified to constant pressure heat addition (i.e. the volume varies whilst the pressure stays the same), and this difference in volume during the combustion phase is called the cut-off ratio. As the cut-off ratio increase, so thermal efficiency (nu_t) decreases, thus as power increases thermal efficiency drops - the opposite of a gasoline engine.
Hopefully this will give you an insight into how complex engines are - there is no rule that says diesels are worse than petrols as such. Because of the lack of revs and the constraints that applies to gearing, combined with a heavier engine, and reduced thermal efficiency at WOT means that diesels are not ideal for racing unless the series has rules to contradict gasolines advantage. Diesel however is, from an emissions point of view, and a part load fuel economy point of view, superior (assuming you can trap the carcinagenic particulate soot generated by diesels).
Thermal Efficiency = (Power x 2) / (bsfc * rev/second), and a diesel will often get higher, but not necessarily.
The sohpisticated diesel injection systems do not 'make it go like a petrol engine', it is primarly a NOx and Knock resistance matter, though of course it helps performance over indirect injection.
However, you are right in saying that similar sized/specced petrol and diesels will almost certainly allow the petrol to win in a straight fight (assuming sensible gearing for both cars). However, as diesels routinely run with a compression ratio of 20:1 or more they can't rev as highly (as the piston and conrod as to be stronger, and thus heavier), which severely limits a diesel in outright performance.
The MAIN advantage with diesel engines is the fact that a diesel isn't throttled. This means there is less low pressure inlet manifold air to perform work on the piston (known as pumping losses) whilst at part load. This, in turn, means that the diesel ends up more fuel conversion efficiency at part load.
For a given compression ratio the diesel actually has a much lower thermal efficiency compared to gasoline, but thermal efficiency increases with compression ratio -> it turns out that a gasoline engine at about 9:1 has the same nu_t as a diesel at 20:1 (very rough figures). Diesel combustion may be roughly simplified to constant pressure heat addition (i.e. the volume varies whilst the pressure stays the same), and this difference in volume during the combustion phase is called the cut-off ratio. As the cut-off ratio increase, so thermal efficiency (nu_t) decreases, thus as power increases thermal efficiency drops - the opposite of a gasoline engine.
Hopefully this will give you an insight into how complex engines are - there is no rule that says diesels are worse than petrols as such. Because of the lack of revs and the constraints that applies to gearing, combined with a heavier engine, and reduced thermal efficiency at WOT means that diesels are not ideal for racing unless the series has rules to contradict gasolines advantage. Diesel however is, from an emissions point of view, and a part load fuel economy point of view, superior (assuming you can trap the carcinagenic particulate soot generated by diesels).
Now that's a classic high quality Tristan post. 
Well delivered!
Wish I had something to argue with you about, but....
Well delivered!
Wish I had something to argue with you about, but....
Turbo's are crap, and lag is caused by fish in the 'works'. Argue away matey!
Diesels produce less force over time
(sorry insider)
A few things about this post:
Firstly, I've not seen more than 2-3 posters here with genuine understanding of petrol and diesel engines. Too much petrolhead bashing diesels crap in the air.
Secondly, there is still no way to directly compare diesels and petrols even today. This is simply a function of technological history. Petrols had more than a century of incremental developments vs disesels. Automotive diesels used in 4x4s, sedans, etc have remained underdeveloped until the past decade or so. The fact that Common-rail/DDI diesels are such recent inventions proves this.
FYI, GDI (direct petrol injction) is aleready in existance for about a decade (Mitsubishi GDI in Pajeros being the best example). Yes, the 3.5L GDI Pajero engines are about 10% more power and torque and 30% less emmsions than a mechanically equivilant MPI(Multi-point injection) engine. But the real jump is the diesel.
Example:
Mitsubishi Motors Diesel 4D56
-2477cc
The original 4D56 had 147nm@2500 and 72ps@4200, 4700 redline.
The turbo-intercooled of the 4D56 had about 200nm@2000 and 99ps@4000, 4500 redline.
The latest iteration of the 4D56 is built on the same fundamental engine block design turbo-intercooled with the addition of Hyper Common-Rail Injection and DOHC in place of the old SOHC head. The result:
136ps@4000 and 314nm@2000, 4500 redline. 11.8L/100km in URBAN driving mode in a 1890kg kerb weight pick-up truck (new L200 or Triton, depending on the market).
Or one could opt for the power upgrade pack for over 160ps, all while complyig with EU-4 emmison standards.
Note that the basic engine block design and capcity have remained unchanged. And believe me, I've tried the original 72ps engine. though underpowered, it has absolutely no hestitation to rev towards its 4700rpm redline. With turbo-intercooler, high pressure fuel injection and DOHC, itwould obviously rev even better.
Note that diesels are practically more efficient since they run at maximum intake airflow almost continuously, so the only mechanism for rev and power output control is rate of fuel intake. As long as the A/F ratio remians greater than stoichometric, diesel efficiency is always superior to petrol. For diesels, fule consumption is much more directly related to power output.
Also note that turbo petrols are forced to run low compression ratios, which again kills effieciecy. Petrol turbo engines need to run rich all the time to avoid detonation. Diesels actually improve in efficiency with forced induction, since more air only means leaner A/F ratio if fuel intake rate remains static. Or one could simply maintain A/F ratio and enjoy greater performance with no loss in fuel-power efficiency. Try that with a petrol engine and you'll detonate the engine to smitherines.
In lay man terms, diesels get all the benefits of turbos and none of the conmy tradeoffs, a win-win deal. Petrols are heavily compromised in this respect. The fact that diesel blocks and internals are much stronger than their petrol counterparts only ensures superior reliability. in fact, some diesels don't break in completely until over 100,000km.
From the emmisions point, even the oldest NA 4D56 won't smoke or smell, except on cold starts. Note it doesn't even use a soot filter. The smoky diesel syndrome petrolheads blaber about are just the result the result of poor maintainance and injection settings. people are notorious for skipping oil and filter changes and other routine service. I've tried to get a warmed up NA 4D56 to smoke at full throttle at redline (4700rpm). No luck.
Conclusion: Diesels are at the infancy of their development and their superiority over petrol is a technological inevitability.
And please, informed replys only. This is an LFS (aka hardcore sim) forum, not NFS:Most wanted/Underground. Last thing we need is underinformed opinions to ruin the realist atmosphere of LFS.
Hope this helps everyone.
Firstly, I've not seen more than 2-3 posters here with genuine understanding of petrol and diesel engines. Too much petrolhead bashing diesels crap in the air.
Secondly, there is still no way to directly compare diesels and petrols even today. This is simply a function of technological history. Petrols had more than a century of incremental developments vs disesels. Automotive diesels used in 4x4s, sedans, etc have remained underdeveloped until the past decade or so. The fact that Common-rail/DDI diesels are such recent inventions proves this.
FYI, GDI (direct petrol injction) is aleready in existance for about a decade (Mitsubishi GDI in Pajeros being the best example). Yes, the 3.5L GDI Pajero engines are about 10% more power and torque and 30% less emmsions than a mechanically equivilant MPI(Multi-point injection) engine. But the real jump is the diesel.
Example:
Mitsubishi Motors Diesel 4D56
-2477cc
The original 4D56 had 147nm@2500 and 72ps@4200, 4700 redline.
The turbo-intercooled of the 4D56 had about 200nm@2000 and 99ps@4000, 4500 redline.
The latest iteration of the 4D56 is built on the same fundamental engine block design turbo-intercooled with the addition of Hyper Common-Rail Injection and DOHC in place of the old SOHC head. The result:
136ps@4000 and 314nm@2000, 4500 redline. 11.8L/100km in URBAN driving mode in a 1890kg kerb weight pick-up truck (new L200 or Triton, depending on the market).
Or one could opt for the power upgrade pack for over 160ps, all while complyig with EU-4 emmison standards.
Note that the basic engine block design and capcity have remained unchanged. And believe me, I've tried the original 72ps engine. though underpowered, it has absolutely no hestitation to rev towards its 4700rpm redline. With turbo-intercooler, high pressure fuel injection and DOHC, itwould obviously rev even better.
Note that diesels are practically more efficient since they run at maximum intake airflow almost continuously, so the only mechanism for rev and power output control is rate of fuel intake. As long as the A/F ratio remians greater than stoichometric, diesel efficiency is always superior to petrol. For diesels, fule consumption is much more directly related to power output.
Also note that turbo petrols are forced to run low compression ratios, which again kills effieciecy. Petrol turbo engines need to run rich all the time to avoid detonation. Diesels actually improve in efficiency with forced induction, since more air only means leaner A/F ratio if fuel intake rate remains static. Or one could simply maintain A/F ratio and enjoy greater performance with no loss in fuel-power efficiency. Try that with a petrol engine and you'll detonate the engine to smitherines.
In lay man terms, diesels get all the benefits of turbos and none of the conmy tradeoffs, a win-win deal. Petrols are heavily compromised in this respect. The fact that diesel blocks and internals are much stronger than their petrol counterparts only ensures superior reliability. in fact, some diesels don't break in completely until over 100,000km.
From the emmisions point, even the oldest NA 4D56 won't smoke or smell, except on cold starts. Note it doesn't even use a soot filter. The smoky diesel syndrome petrolheads blaber about are just the result the result of poor maintainance and injection settings. people are notorious for skipping oil and filter changes and other routine service. I've tried to get a warmed up NA 4D56 to smoke at full throttle at redline (4700rpm). No luck.
Conclusion: Diesels are at the infancy of their development and their superiority over petrol is a technological inevitability.
And please, informed replys only. This is an LFS (aka hardcore sim) forum, not NFS:Most wanted/Underground. Last thing we need is underinformed opinions to ruin the realist atmosphere of LFS.
Hope this helps everyone.
Very interesting post 
Everything I've ever read / studied indicated a general increase in fuel economy when fitting a proper turbocharging system to a gasoline engine. Your post seemed to contradict this somewhat, so I have a few questions perhaps you could answer for me to shed some light on the matter:
Isn't the overall mean effective cylinder pressure what really matters in terms of output vs consumption? Therefore who cares if a gas engine has a slightly lower compression ratio to compensate for some intake pressure... Beyond that, one can safely run "standard" compression with less pressure and acheive the same result either way....
The Beta II block in my car has a stock compression of 9.5:1.... I can acheive the exact same result by either:
a) lowering compression to 8.5:1 and running ~11psi
b) running 7psi on stock compression
I didn't do the math, but that should be pretty close.
Everything I've ever read / studied indicated a general increase in fuel economy when fitting a proper turbocharging system to a gasoline engine. Your post seemed to contradict this somewhat, so I have a few questions perhaps you could answer for me to shed some light on the matter:
Isn't the overall mean effective cylinder pressure what really matters in terms of output vs consumption? Therefore who cares if a gas engine has a slightly lower compression ratio to compensate for some intake pressure... Beyond that, one can safely run "standard" compression with less pressure and acheive the same result either way....
The Beta II block in my car has a stock compression of 9.5:1.... I can acheive the exact same result by either:
a) lowering compression to 8.5:1 and running ~11psi
b) running 7psi on stock compression
I didn't do the math, but that should be pretty close.
An interesting observation, but easily explained.
Most petrol roadcars IRL run rich due for detonation resistance and easier NOx emmision control. In essence, they have really poor airflow rates for their fuel flow settings. In your case, the turbo simply adds airflow rate to the equation, leaning out the A/F ratios a bit if your fuel rate remains the similiar, causing more complete combustion and thus more power and torque. The lessened need to depress the throttle goes a LONG way to explaining fuel economy increase. Conservation of energy always applies, so there is no free energy, just better extraction of the fuel's potential energy. Hopefully you've not gone TOO lean or massive detonation would result. I've not seen a high pressure turboed petrol car that experiences improved fuel to power conversion efficiency after compression reduction to help the relatively weak petrol blocks and internals to cope with massive cylinder pressures.
Please read the quality post at the top of page 4. Obvioulsy, lower compression reduces thermal efficiency. By the way, high pressure diesel injection improves efficiency by squirting fuel through ultra fine holes(like those many hole in your showerheads but MUCH finer), vastly improving fuel atomization. The true secret to better power effieciency is the more complete burn of diesel. 2 step injection regimes help too.
Conclusion:
Diesel + turbo equals complete synergy.
For already highly tuned petrols running A/F ratios on the leaner side, turbos are guaranteed to reduce efficiency.
Most petrol roadcars IRL run rich due for detonation resistance and easier NOx emmision control. In essence, they have really poor airflow rates for their fuel flow settings. In your case, the turbo simply adds airflow rate to the equation, leaning out the A/F ratios a bit if your fuel rate remains the similiar, causing more complete combustion and thus more power and torque. The lessened need to depress the throttle goes a LONG way to explaining fuel economy increase. Conservation of energy always applies, so there is no free energy, just better extraction of the fuel's potential energy. Hopefully you've not gone TOO lean or massive detonation would result. I've not seen a high pressure turboed petrol car that experiences improved fuel to power conversion efficiency after compression reduction to help the relatively weak petrol blocks and internals to cope with massive cylinder pressures.
Please read the quality post at the top of page 4. Obvioulsy, lower compression reduces thermal efficiency. By the way, high pressure diesel injection improves efficiency by squirting fuel through ultra fine holes(like those many hole in your showerheads but MUCH finer), vastly improving fuel atomization. The true secret to better power effieciency is the more complete burn of diesel. 2 step injection regimes help too.
Conclusion:
Diesel + turbo equals complete synergy.
For already highly tuned petrols running A/F ratios on the leaner side, turbos are guaranteed to reduce efficiency.
Looking at your profile tells me that you are old enough to drive so there's one question I need to ask you - Have you ever driven a diesel??
My dad has owned 2 and the are amazing!! The Audi A4 1.9 Tdi Quattro was OMG!! It had so much torque (apparently, in low revs it has same torque as a Boxster S!!) and it also looked great with the sporty body kit, Dolphin grey metallic and carbon look to go along with the great Bose sound system - All of the things avaliable in the petrol version too!!
The 2nd diesel was the less exciting but still fun BMW 320D SE (52 Plate) - Not anywhere near as sporty and good looking and handling as the A4 but it was quicker as it only had 5 gears and was fun apart from the fact that the TC cut in way too ferociously and quickly so that stopped the fun a bit!!
My dad said he would stick with Diesels... Now he has a Merc C200 Kompressor Estate which he drifts round corners in and we have the new Audi TT Coupe 1.8T on order (apparently the 1.8T is better and "rawer" than the 3.2 version and has the same engine as the Golf GTI)... As you can see by the post - I speak just as highly about the diesels as i do about the petrols so maybe those of you who aren't sure about diesels should try one or maybe if you tried a turbo-less one then try one with a turbo! I'm sure your views will be different.
Sam (Phew!)
Edit: Yes - they may sound awful but some are actually ok sounding - the ones with the bigger engines in particular!!
Speaking of diesel sounds, I happen to drive an NA Diesel Pajero and it sounds absolutely beautiful. Who needs ridiculously loud exhausts on some tiny ricer engine when the NA 4D56 already emits extremly throaty sounds? A turbo would attenuate some of the NA roughness, but a freer flowing 2.25inch exhaust would restore the throatiness without the rougher higher frequecy sound spectrum, all while improving power, torque, response and fuel efficiency. All this could be done without exceeding 85dB even at full throttle and oad.
Seriously, 4WD and other private use diesel engines are much better representatives of how good diesels could sound. Please, do not lock yourselves into this diesel sound=UPS truck sound dogma.
Go to the Borla or Magnaflow websites and sample a few turbodiesel exhaust notes. Musical.
Seriously, 4WD and other private use diesel engines are much better representatives of how good diesels could sound. Please, do not lock yourselves into this diesel sound=UPS truck sound dogma.
Go to the Borla or Magnaflow websites and sample a few turbodiesel exhaust notes. Musical.
Magnaflow site - I saw an RS4 about 2 days ago and I thought that was the best sounding car i have ever heard... Shove a Magnaflow on the back and omg
I don't think that makes too much sense, but I could be wrong. I'm not as informed as you appear to be, but I was under the impression that typical modern cars run 14.7:1 edit: A/F ratio most of the time specifically FOR emissions, since stoichometric obviously is complete (theoretical) combustion. It's relatively common knowledge that slightly richer edit: than stoich(not leaner!) mixtures are ideal for edit: higher output alone, new cars with decent heads usually benefit from around 13:1 edit: A/F ratio for higher output at WOT.
My fuel rate at even 7PSI would need to be almost 50% greater (save for less mass due to heating of the air) to maintain ideal combustion, running lean under pressure would be engine suicide.
You might note that I commented on it immediately after it was written over 2 months ago
Indeed it is a quality post.
...
Yes, I realise that turbocharging diesels is excellent, and I understand your point about that.
I'm not convinced about the rest of your information yet.
I forgot to specify that all the benefits in fuel economy that so called "proper" turbocharging entails the use of low pressure turbos which, for petrols, is about 5-7psi and never more than 10psi. The high pressure turbos such as 1 bar (14.7psi) setups will masssively increase airflow and thus power reliability if compression was lowered (usually to something like 9:1 or LOWER) with the con-rods and pistions replaced with stronger billet/forged units. unfortunately, the lower compression negates some of the thermal effieciency gains of higher intake and effective compression pressure, so from the power per fuel burned point of view, high press. turbos are guaranteed to reduce fuel to power conversion efficiency.
As to why road cars run rich and NOx emmsion concerns. Firstly, one must understand where the NOx comes form.
The NOx is generated due to the fact that air is not pure O2. The spark park ignites the petrol and air mixture, but unfortunately the Nitrogen (air is more than 70% N2!) also gets oxidized in the process, hence NOx. With richer mixtures, there's less oxygen to oxidize N2, thus less NOx. That massively reduces the NOx emmsion problems.
So, how would you deal with the unburnt hydrocarbons? Behold the 3 -way catalytic converter! Catalyses the chemical reactions that change unburnt hydrocarbons, CO and other products of incomplete combustion to much more benign CO2 and H2O.
Another major reason for richness is cylinder cooling and also overall temperature regulation of the combustion chamber. Obviously, regulation of temps is crucial for reliability. Unburnt fuel happens to be a good coolant. The best example I can remember off hand is the 911 turbo engine. It's well known for very rich A/F mixtures at higher revs to stabilize engine temp at the cost of absolute top end performacne. The above reasons of NOx regulation apply too.
One of the problems with lean burn seen in diesels and GDI (aka dieselized petrol) is NOx generation caused by oxygen rich burn. This is currently reduced markedly via NOx scrubbers that deoxidizes NOx to its Nitrogen and oxygen components. The best example of a car with this system is the current 3.5L GDI engine of the European spec Pajero. Obviously, it has also been used and will only bettered for current High Performance Diesels.
As for optimal power, yes, stoich ratios are theoretically ideal, but the real physical limitation is fuel atomization for better fuel to O2 contact and more complete burn. This goes a long way to explaining why diesels benefit so much from high pressure injection sysytems. Practically, just slightly rich ratios are the best compromise for both relability and power. Lets just say I've seen enough dyno shootouts end up in massive engine kabooms due to leaning A/Fs to squeeze that last bhp. As the A/F leans, so does the ignitability, so unless you could massively cool the combustion chamber whilst compression, detonation is inevitable. This is why the GDI engines can run 13:1 comp. ratios and ultra lean 30:1 A/Fs. The direct injection system allows better combustion chamber cooling and avoids preheating fuel at the ports, avoiding detonation.
Ultimately, the otto cycle is limited by the fact that it uses A/F mixtures instead of swuirting fuel at the right moments. Compression can never rise too high since petrol is notorious for spontaneous ignition.
If the current diesel fuel atomizaton improvements continue, the A/F could be adjusted richer and more towards stoich ratios without risk of generating excess soot.
And no, your average econobox does NOT run 14.7:1 comp. ratios, unless it happens to posses diesel like (aka insanely strong) block, head and internals and the aforementioned excellent detination control. More like 10.5:1 on average. For example, the high rev engine that the current NA Lotus Exige uses (from Toyota) has a comp ratio of approx. 11:1 and thats considered on the high side. Don't compare it to your typically weak aluminum alloy econoblocks. That engine block is composed of metal-matrix composites, F-1 technology that was banned with advent of the current V8 engines. If it wasn't banned, redlines would be around 24,000rpm instead of the currently "low" 20,000rpm.
As to why road cars run rich and NOx emmsion concerns. Firstly, one must understand where the NOx comes form.
The NOx is generated due to the fact that air is not pure O2. The spark park ignites the petrol and air mixture, but unfortunately the Nitrogen (air is more than 70% N2!) also gets oxidized in the process, hence NOx. With richer mixtures, there's less oxygen to oxidize N2, thus less NOx. That massively reduces the NOx emmsion problems.
So, how would you deal with the unburnt hydrocarbons? Behold the 3 -way catalytic converter! Catalyses the chemical reactions that change unburnt hydrocarbons, CO and other products of incomplete combustion to much more benign CO2 and H2O.
Another major reason for richness is cylinder cooling and also overall temperature regulation of the combustion chamber. Obviously, regulation of temps is crucial for reliability. Unburnt fuel happens to be a good coolant. The best example I can remember off hand is the 911 turbo engine. It's well known for very rich A/F mixtures at higher revs to stabilize engine temp at the cost of absolute top end performacne. The above reasons of NOx regulation apply too.
One of the problems with lean burn seen in diesels and GDI (aka dieselized petrol) is NOx generation caused by oxygen rich burn. This is currently reduced markedly via NOx scrubbers that deoxidizes NOx to its Nitrogen and oxygen components. The best example of a car with this system is the current 3.5L GDI engine of the European spec Pajero. Obviously, it has also been used and will only bettered for current High Performance Diesels.
As for optimal power, yes, stoich ratios are theoretically ideal, but the real physical limitation is fuel atomization for better fuel to O2 contact and more complete burn. This goes a long way to explaining why diesels benefit so much from high pressure injection sysytems. Practically, just slightly rich ratios are the best compromise for both relability and power. Lets just say I've seen enough dyno shootouts end up in massive engine kabooms due to leaning A/Fs to squeeze that last bhp. As the A/F leans, so does the ignitability, so unless you could massively cool the combustion chamber whilst compression, detonation is inevitable. This is why the GDI engines can run 13:1 comp. ratios and ultra lean 30:1 A/Fs. The direct injection system allows better combustion chamber cooling and avoids preheating fuel at the ports, avoiding detonation.
Ultimately, the otto cycle is limited by the fact that it uses A/F mixtures instead of swuirting fuel at the right moments. Compression can never rise too high since petrol is notorious for spontaneous ignition.
If the current diesel fuel atomizaton improvements continue, the A/F could be adjusted richer and more towards stoich ratios without risk of generating excess soot.
And no, your average econobox does NOT run 14.7:1 comp. ratios, unless it happens to posses diesel like (aka insanely strong) block, head and internals and the aforementioned excellent detination control. More like 10.5:1 on average. For example, the high rev engine that the current NA Lotus Exige uses (from Toyota) has a comp ratio of approx. 11:1 and thats considered on the high side. Don't compare it to your typically weak aluminum alloy econoblocks. That engine block is composed of metal-matrix composites, F-1 technology that was banned with advent of the current V8 engines. If it wasn't banned, redlines would be around 24,000rpm instead of the currently "low" 20,000rpm.
First, thanks for the informative post again...
Second you missed my point(s) so I edited my post for clarity.
Any dummy knows normal gasoline "road cars" don't run 14.7:1 compression ratios :hihi:
Second you missed my point(s) so I edited my post for clarity.
Any dummy knows normal gasoline "road cars" don't run 14.7:1 compression ratios :hihi:
Sorry about that. What you say about the 14.7 stoich A/F ratio is theoretically true. However, one must also consider all the real world factors that properly serviced cars never face. IRL, many owners are notorious for skipping or severely extending routine sevices such as oil changes. Americans (in genegeral, not everyone) have a notorious record of skipping service. So do Malalysians (goes a looong way to explaining why so many diesels smoke so badly there). Asssuming that fuel atomization is near ideal, stoich gives the best power. However, as I've said, fuel happens to be a good combustion chamber cooler. For reliability and safety, OEMs usually err on the safe (aka rich) side. The last thing a car manufacturer needs is to deal with trashed engines.
The restrictive OEM intakes and exhausts to practically eliminate all engine noise doesn't help breathing either. For cars such as Porsche 911 turbos, the ECU is usually setup to run leaner A/Fs at high revs for top end power (if airflow was constant). And again as stated, lower combustion temps are necessary to provide a buffer against typical neglect. But seriously, how many of us would use Mobil 1 5W-30 quality oil on a Toyyta Echo? Lower temps are insurance against such variables.
To seal the point abut rich A/F mixtures, try passing the latest emmsions tests without the cat converter. Your unburnt hydrocarbon concentrations are guaranteed to soar. Emmisions control, even today, is still mostly about after treatment, not ultimate thermal effficiency. Unless your gasoline engine happens to be a GDI or FSI(european manufacturer name for the same tech) running in its lean burn mode, don't expect stoich or close to stoich in anything less highly tuned than the N/A Lotus Exige's engine. Since fuel economy ratings are miles per gallon or liters per 100kms, they are poor pointers when it comes to comparing the power generation efficiencies of engines.
Oh, the GDI ensines run very close to stoich A/Fs when it runs at maximum power mode.
As you all should know, petrols generate maxiumum power efficiency at WOT. But how often can you actually use WOT in your average city traffic? Secondly, even racers don't go WOT whenever on throttle. Try running a WRC Monte Carlo rally stage at WOT only. See you at the bottom of the hill (if we could actually FIND you). Please, don't mistake this as a personal attack. I'm just trying to illustrate a point as clearly as possible.
Thanks for pointing out my oversight, Ball-Bearing Turbo! Hope this lays your doubts to rest. I'll gladly clarify anything that needs clarifying.
The restrictive OEM intakes and exhausts to practically eliminate all engine noise doesn't help breathing either. For cars such as Porsche 911 turbos, the ECU is usually setup to run leaner A/Fs at high revs for top end power (if airflow was constant). And again as stated, lower combustion temps are necessary to provide a buffer against typical neglect. But seriously, how many of us would use Mobil 1 5W-30 quality oil on a Toyyta Echo? Lower temps are insurance against such variables.
To seal the point abut rich A/F mixtures, try passing the latest emmsions tests without the cat converter. Your unburnt hydrocarbon concentrations are guaranteed to soar. Emmisions control, even today, is still mostly about after treatment, not ultimate thermal effficiency. Unless your gasoline engine happens to be a GDI or FSI(european manufacturer name for the same tech) running in its lean burn mode, don't expect stoich or close to stoich in anything less highly tuned than the N/A Lotus Exige's engine. Since fuel economy ratings are miles per gallon or liters per 100kms, they are poor pointers when it comes to comparing the power generation efficiencies of engines.
Oh, the GDI ensines run very close to stoich A/Fs when it runs at maximum power mode.
As you all should know, petrols generate maxiumum power efficiency at WOT. But how often can you actually use WOT in your average city traffic? Secondly, even racers don't go WOT whenever on throttle. Try running a WRC Monte Carlo rally stage at WOT only. See you at the bottom of the hill (if we could actually FIND you). Please, don't mistake this as a personal attack. I'm just trying to illustrate a point as clearly as possible.
Thanks for pointing out my oversight, Ball-Bearing Turbo! Hope this lays your doubts to rest. I'll gladly clarify anything that needs clarifying.
would be interesting to see a desiel up against a XRT/FXO/RB4
Just make the FXO diesel 
FWD + massive torque curve of turbodiesel = 3 minutes of front tire life
Diesel car
(208 posts, started )
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