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It is normal that EGR is reduced at high rpm. Another factor might be that the capacity of the NOx storage catalyst is limited. If the catalyst is almost “full”, I doubt that regeneration of the catalyst could be done if the driver starts very aggressive driving at highway in that situation. There are some thermal limitations for running an engine slightly below lambda 1 (for NOx regeneration) at very high load. This might explain the great variation between their tests. It is obvious that they tried their best to frame BMW. Given the fact that TÜV Süd has thoroughly investigated this car, I would doubt that there is any defeat device in the software. Everything that DUH showed can be explained by applying some knowledge and common (engineering) sense. Having said that, one could add that there will always be off-cycle driving conditions when a grey zone is entered and some measures have to be taken to protect the engine and aftertreatment. This is allowed in the regulation. The same can also be seen for gasoline engines. One such example is the full load enrichment, which also increase emissions, albeit other emission components than NOx (e.g. CO, HC and PM). Without fuel enrichment many engines would destroy the catalyst, with even worse emissions as a result.
@Thomas Pedersen I can agree with you, although I do not have so many horses in my Ford Focus as you have in your car. It almost never happens that I break 3000 rpm. Normal shift point is just under 2000 rpm. In dense traffic, I would run over the car in front of me if I went over 3500 rpm.
The emission limit for on-road measurements is not 80 mg/km; it is 168 mg/km. Axel Friedrich, a “global” expert on emissions, should know this but one could presume that he chose not to mention this, since it would speak against his arguments. Moreover, the 168 mg/km limit is enforced for NEW vehicles starting this autumn and for ALL vehicles in 2019. The limit does not apply retroactively, i.e. on cars manufactured in 2016, such as this car. If we look at data not so biased as this study, we find that, e.g. the German magazine ams, has ranked BMW as the best one of all manufacturers tested so far. We can also note that the certifying body TÜV Süd backs up BMW. They have tested a similar car of the same model. Neither in the lab nor in on-road measurements could they see any signs of illegal defeat devices. Overall, the tested vehicles showed a very robust emission behavior. We can also note that all new (I presume?) BMW diesel engines will have more advanced emission control than this car, which only has a NOx storage catalyst. New engines have a combination of NOx storage and SCR catalysts. One example is the BMW 520d that (so far) has the lowest level of all diesel cars tested by ams. Starting late this year, BMW is also introducing a new engine with; presumably, even lower emissions than the mentioned 520d, which had the old engine but SCR catalyst.
Well, this is no proof. They have not investigated the WLTP. Find a scientific study! In my opinion WLTP is the best we have for the time being. The claim that US EPA figures are right is a joke. How could a test procedure and driving pattern from the 70's be representative for modern vehicles? No way! Not even with a correction factors.
@HarveyD. You have fudged yourself! A Nissan sold in your country has not been certified according to WLTP!!! US EPA has no plans whatsoever to introduce WLTP in the near future. WLTP was introduced in Europe from September 1 this year. For new cars. Next year for all cars. WLTP is based on logging of real-life driving style in many countries. This was done fairly recently. Your Nissan has been certified according to FTP-75, which is based on logging in the early 70’s. In contrast to NEDC and FTP-75, WLTP has also plugged many loopholes in the testing methodology. Those who are not completely blind have already seen (on this site) that fuel consumption levels for cars certified according to WLTP are much, much higher than for corresponding cars certified according to NEDC. Show me some reference that proof that WLTP is easy to fudge.
The best use of e-H2 would be to put it directly into the refinery, where there already is a lack of H2. Efficiency would be much higher and cost would be much lower. Or, is this route too obvious to be of any interest?
@Mahonj Why is WLTP too easy to fudge? Where did you get that from??? Reference, please! (You could say that about NEDC, though.)
Why would Lamborghini bother about emissions and GHGs? They aim for something completely different.
Organic fluids are not well-suited for high temperatures and pressures, so in case a piston expander is used, water or CO2 would be better options. With water, dimensions could be very small as can be seen in the two references below. At 250 bar, 450°C and 6 000 rpm, you get 1 200 kW per liter of displacement (fig. 8 in the first reference). That is sufficiently small for most applications and certainly much smaller than any conventional ICE today.
It seems as most of you are assessing this invention as if it would be almost production-ready unit. It is just a laboratory set-up, which, at most, qualifies as a proof-of-concept. For example, you cannot make a compact unit if you run at maximum at peak velocity of 0.69 m/s. A free-piston unit should achieve (mean) piston speed in the range of (or above!) modern light and heavy-duty engines, i.e. at least >10 m/s. Modern steam engine concepts also aim at similar piston speeds. Operating at higher pressures also decrease the size considerably. Note the comment: “…the researchers will next investigate the effects of higher pressure and operation frequency on the FPLG…”. Furthermore, note that steam engines are, per definition, 2-strokes, which gives double the number of power strokes compared to a 4-stroke design (in this case, without the drawbacks that plague 2-stroke ICEs). A power cylinder of a steam engine does virtually no compression work in the cylinder; only expansion, which also increase power density. With all positive factors combined, there is potential for very high power density, which also modern steam engines prove by being much more compact that a corresponding 4-stroke gasoline or diesel engine. Whether they will succeed in developing the concept to a commercial unit is another story.
Current hydrofracking in the USA for producing oil and gas is also insane.
The more you pump (or mine) out of the ground, the more CO2 we will have in the atmosphere. This will result in cheap fuel, no restrictions for gas guzzlers and, as a result, an increase of global warming. The only hope for the globe is that Americans eventually (?) will understand the connection between global warming and the hurricanes that tend to plague the country.
VW wants to make money. Tesla does not make any money.
So, this is what we have been waiting for during so many years...
Nice! However, I would like to know more about the exhaust aftertreatment system. Is it similar to the diesel version or have they done anything to improve methane oxidation and catalyst durability?
So, if our cars have lower fuel efficiency we drive less and consume less fuel, or?... Of course this study is as biased as a study ever can be.
There is no fundamental difference between the "B-cycle" and the Miller cycle. I presume this coined expression is just BS from the marketing department.
First, I realize that I have forgotten to give Mazda credit for bringing this concept to full production. I can only recall a few attempts to utilize HCCI in the past in production engines and one familiar example, a Honda motorcycle, had a 2-stroke engine. This would be the first production 4-stroke gasoline engine with HCCI and Mazda should have credit for that. I think the main achievement here is the switching between HCCI and conventional mode. The “highly responsive air supply unit” might be the key here, albeit that Mazda does not elaborate much on this topic.
@Brian P As you noted, the graph is illustrative and perhaps, somewhat deceptive. You should realize that a “good” diesel engine can achieve double the BMEP (~2 500 kPa) of the Skyactive-X. In a “normal” driving cycle, average engine load corresponds to a BMEP of approximately 200 kPa. Due to the higher maximum BMEP, this equals 400 kPa for the diesel engine. Thus, the most reasonable comparison of fuel consumption at low load is to compare the level at 200 kPa for Skyactive-X with 400 kPa for a diesel engine (i.e. the same load percentage). If you do this simple math, you will find that a diesel engine is far better than Skyactive-X also at low load. The diesel cycle is the most efficient thermodynamic cycle for piston engines and the most efficient “practical” heat engine of any kind. (Yes, you could argue that diesel-atkinson cycle, or miller system - whatever you prefer to call it - would be even better but this is just a variation of the basic diesel cycle.) In over 100 years, nobody has actually come up with something that is more efficient; in fact, not even equal.
So, this concept could also have been coined PTDE: part-time diesel engine (but running on gasoline). The HCCI area is significantly smaller than I had expected. The engine is not as advanced as I had thought (and that previous articles indicated). If you compare with the Skyactive diesel at full load, the fuel consumption penalty for Skyactive-X is quite dramatic. Why the Skyactive diesel curve ends at a BMEP level of 1000 kPa is beyond my comprehension. The diesel has higher BMEP. Perhaps Mazda simply would not like to show that the gap is even bigger at maximum BMEP for the diesel engine. Confounding! Furthermore, if you would compare to a (competitor) state-of-the-art diesel, you should note that such and engine has maximum BMEP at 2500-3000 kPa. With the downsizing (of the diesel engine) this implies, Skyactive-X would lose by quite some margin. Scaling according to load percentage on the x-axis, instead of showing absolute values, is the most reasonable comparison when BMEP levels differ so much as in this case. Comparing apples-to-apples data presumably would also show that, even at light load when HCCI is implemented, Skyactive-X would not reach diesel level. All-in-all, Skyactive-X still seems to be quite far from reaching the efficiency of a diesel engine. If the Skyactive-X engine was used in a hybrid system that shift load to higher BMEP levels, its advantage would be smaller compared to conventional gasoline engines. The gain compared to Atkinson/Miller gasoline engines would be far less – if any – in a full hybrid system. In view of what I mentioned above, I am also surprised by the relatively low maximum BMEP (1300 kPa!). However, this is a classic problem for all gasoline HCCI concepts and it seems as Mazda has not overcome that. I suppose that high-load aftertreatment will be conventional TWC, potentially supplemented by GPF for Europe later.
“About time”, one could say, when we note that the public opinion seems to have wanted this for a very long time. People in general do not understand that it is a very long process before a new regulation can come into force. As I can recall, work on the WLTP test cycle has been going on for at least for 10 years and the process for RDE was almost as long. RDE has noting specifically to do with the VW scandal but it might have had a minor impact on the process most recently. For sure, this has justified the complex - and expensive - RDE testing; no debate about that any more. On the background on what EU has done, we can see the US EPA will still continue to use a test procedure that was conceived in the 1970’s. The old FTP cycle has little resemblance with modern driving style, yet EPA will still use it at least to 2025. This is stunning, since USA has participated in this work. The basic idea with “Worldwide Harmonized…” was that it would be used… around the globe. But perhaps the main idea as to why EPA has not adopted WLTP is some kind of protectionism or an act to favor US auto industry. Not invented here… The first thing that will be immediately noted is that fuel consumption in the WLTP will be closer do “real-world” fuel consumption. Yet one should note that “real-world” fuel consumption is different for every customer. “Worldwide Harmonized” also means that the test cycle is a compromise between different driving styles around the world. Nevertheless, comparisons between cars will be more realistic in WLTP. On the long run, RDE will decrease “real-world” emissions and thus, improve ambient air quality. It will also make competition more “fair” and close a couple of loopholes. This is by no means the end of the development. The next step will most likely be much simplified RDE tests where sensors will be used instead of advanced laboratory instruments. This would enable more tests at a significantly lower cost, i.e. more cost-effective testing. Work is already going on in this field and tests are promising. The third step could be that such sensors are permanently mounted on cars and log emissions for long periods, i.e. weeks or months. Data will be sent wireless to a server for “big data” analysis. The fourth and (perhaps) the final step could be that such sensors are integrated in the engine emission control system and used for OBD/OBM/OBS, or whatever you would like to call it.
Well, this one is not dirty but it remains to convince customers about that.
EquiNOx. Isn't that a cool name for a diesel car?
@DJ_D Sorry to say, it is not that easy. Flame speed is definitely an issue with HCCE and PCCI. It is almost like a detonation. It is much, much worse than diesel if you look at pressure rate for cylinder pressure. You would hear this car blocks away. Thus, something must be done to abate combustion noise. You can have low NOx if air excess is high. Yes! HCCI/PCCI can run much leaner than GDI. However, this is not the full story. You have to reduce excess air at full torque (and close to full torque) and then NOx will rise sky-high (any joke about that is on me…). Try to imagine running excess air at 2:1 ratio at full load with high compression ratio and fast combustion. No engine structure in the world could handle such cylinder pressure. It would be much, much higher than for diesel. If you limit cylinder pressure to reasonable levels, power and torque would be a joke and you would have to do a lot of “anti-downsizing” This would ruin fuel economy. Recall research carried out by Huyndai/Delphi. They certainly had to deal with high cylinder pressure and you can find comments from me on that as well in the past on this forum. Furthermore, if you are just marginally on the lean side, TWC will not work. So, in essence, you would have sky-high NOx at high load but conventional aftertreatment would not work. Even if this problem would not be too bad in a conventional test cycle, RDE would kill such an engine. You could imagine replacing excess air with EGR, perhaps gradually, but this is not easy to control. Toyota tried this many years ago with homogenous lean-burn (long before GDI) but the result was not very good. I have tested such cars myself in the laboratory. Needless to say, NOx was much higher than from TWC cars. You could adopt similar aftertreatment as for diesel (NOx-trap + SCR) but it comes at a cost and you would still struggle in off-cycle conditions. In summary, there are a lot of issues to explain. Perhaps Mazda has cracked a couple of the nuts but we have no idea about how they did it.