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Peter_XX
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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.
Sadly, this article does not really say anything about the technology other than using lean burn and a supercharger. I have not read the SAE Paper, I have to admit. They also speak about increasing compression ratio to 18:1 in an older article at GCC. Both increasing CR and using excess air (via supercharging) is beneficial for efficiency. This we also know from diesel engines, i.e. nothing fundamentally new when it comes to thermodynamics. The interesting part is how they control combustion and in particular, knocking and flame speed. This is the Achilles’ heel for gasoline engines but pose no problem for diesels. The main disadvantage of lean burn is the difficulty to control NOx via exhaust aftertreatment. This we also know from experience on diesel engines and, in fact, also on gasoline engines. It was a significant problem on early GDI engines that all operated under lean-burn conditions. Mercedes are one of the few manufacturers who still pursue lean burn on some of their gasoline engines, albeit to my knowledge not on all markets. In summary, this article raises more questions than it answers. If anybody has well-founded technical insights into Mazda’s technology, I am all ears.
The whole idea with mild hybrids is to have a lightweight electrical system, i.e. small motors and batteries. Thus the electric range will be limited to parking garages and similar operation. If you want long electric range, you chose a PHEV. For a mild hybrid, does it matter if the range is, let’s say, 1 or 2 km? Most of the driving will be covered by the combustion engine anyway and the substitution with electricity would be minimal, if we had a plug-in option, which normally is not the case. It does not make much sense either. Battery capacity will be determined by other parameters such as sufficient size for regenerative braking, acceleration, auxiliaries and the requirement for power. Batteries should be kept as small as possible, not only for weight reasons but also to limit incremental cost. If the electric drive system is too heavy, fuel consumption will be significantly penalized in hybrid drive mode. We can clearly see that for PHEVs, where we also have a “conventional” HEV to compare with. The main objective with a mild hybrid is to reduce fuel consumption. If you want to substitute fuel with electricity, there are other (and better) options. I acknowledge that MAHLE, with the limitations of a 48V electric system, seem to have taken this concept to a higher level than before. However, others will follow and challenge. In a few years, this will become the mainstream technology in vehicles. It will provide almost similar fuel economy as a full hybrids but at a fraction of the cost and weight penalty.
Low emissions? Euro V? Hey, come on... Euro VI is the standard since 2013.
Range? Well, perhaps 1500 km with a big fuel tank.
@ai_vin Propane fumigation would have even bigger problems with NOx than diesel engines. This is why we do not see such engines on the road anymore. You simply have to meet the emission limits to sell a vehicle. Propane is best used under stoichiometric conditions where you can use aftertreatment three-way catalyst (TWC). Engine-out emissions are higher than for diesel also in this case but TWC is more efficient aftertreatment than SCR, so we end up with lower tailpipe NOx. Propane and gasoline are roughly equal in this respect. Recall that a gasoline engine also has higher engine-out emissions than a diesel engine. The drawback of stoichiometric combustion is lower efficiency.
The irony here is that heavy-duty vehicles actually are extremely clean compared to light-duty vehicles. A big truck can have lower emissions per kilometer than a small car and if we look at weight-specific emissions, the difference can be monumental. Here, I specifically refer to “actual” on-road (RDE) emission levels of NOx. It may sound strange, since similar SCR technology is used in both cases. I do not have time to elaborate on this at the moment but I can perhaps explain this in a later post. We also know that some Euro 6 light-duty (diesel) vehicles are also clean. Perhaps not fully down to the level of the best gasoline cars but still far below the on-road limit in RDE testing. As pointed out by Carl, a lot of DEF (Adblue in Europe) must be used, particularly so for some heavy-duty vehicles. For reducing NOx, we have three major technologies: EGR (here I would like to include both high-pressure and low-pressure EGR but internal EGR could also be considered), NOx-storage catalyst (NSC or LNT, which you prefer) and SCR. Surprisingly, many “clean” heavy-duty vehicles do not use ANY kind of EGR and LNT is not used in any case to my knowledge. The technology that has enabled this trend is significant improvements in SCR-technology for heavy-duty vehicles during the last couple of years. We are talking about NOx conversion rate of up to 99%. By combining with EGR and LNT, a reduction of NOx by a factor of 10 compared to current Euro VI is not impossible to envision for heavy-duty vehicles. The actual implementation depends on emission regulation (potential Euro VII). It is more difficult to get similar improvements on light-duty vehicles but it will gradually come. Recall that very few cars still have both high-pressure and low-pressure EGR. Some have LNT, some have SCR but very few have both. Carl mentioned BMW but there are a few additional examples. There are also several technologies in the pipeline for increasing SCR efficiency significantly; perhaps not to the level on heavy-duty vehicles but much better than we have today. By reducing engine-out NOx and “after LNT” NOx, the “burden” on the SCR system will actually decrease. Thus, the practical solution of a relatively small Adblue tank and refill only during maintenance can still be obtained. Regarding technology, I do not have any doubt about that very low NOx emissions can be obtained. In addition, it will not cost a fortune. Perhaps the incremental cost will still be too high for the smallest cars but it will not be a show-stopper for medium and larger cars. Recall that some cars already have this technology. Regarding other emissions compounds of health hazard, diesel car are already much better than gasoline cars but this is a discussion we can leave for the moment. The actual “problem” we face today is that some manufacturers have not respected the intention of the regulation, i.e. to give low emissions under all operating conditions. To be honest to the car manufacturers (if one can be than under the circumstances?...), some operating conditions have not been regulated by the legislators, so they could be considered as grey zones. This is the target for the coming RDE regulation. Ironically, Euro 6 cars from the VW group are quite good when it comes to NOx; at least, in comparison to many other car manufacturers. We know they cheated in Euro 5, and in the USA, but this does not concern cars sold today. Finally, we should not underestimate public opinion. This alone can – and will – for sure have a tremendous impact on sales. If people do not want diesel cars, interest from car manufacturers will diminish and development will be stopped.
An electric truck can only transport... batteries.
Well, sd, I understand why you are not employed by the industry. Your idea would be less efficient than the one used by Volvo. Try to figure out why and post your thoughts on this site. Try to find the errors in your own arguments. If you wish, I can help you.
No HarveyD, NOx is not harmful in low concentrations. NO and nitrates/nitrites have very important functions in the body. Without NO, a man could not make love to a woman. That explains all, doesn’t it? Even the lung itself produces NO (exhaled) and at increased levels for some lung diseases. How could inhaling NO in low concentrations be harmful? Although NO2 is more harmful than NO, there is still a threshold level and below this level, no impact is found. NOx is not a poison. This is in stark contrast to toxic emissions, such as e.g. PAH and particles, where no threshold level is found. We should concentrate on such emissions! Of course, we need to lower ambient concentrations for NO2 under the (current) limits in areas with exceedances but there is no rationale for going further than necessary. With measures taken to limit emissions from new vehicles, this will happen nevertheless in a couple of years, simply due to that older polluting vehicles will be scrapped.
All laboratory test cycles include a cold start. It has been so since the 1970's. Thus, a cold start is always part of the test results. The relative impact varies between the different test cycles. In fact, the ”old” European NEDC test cycle is actually one of the toughest (that I know of) in this respect. This furthermore aggravated by the “slow” city driving after start. The impact in the US FTP test is roughly less than half of that in NEDC, since the driving distance per cold start is more than twice as long in FTP. The impact of the cold start will be somewhat less in the new WLTP cycle than in the NEDC cycle. WLTP is based on logging of huge fleets of cars around the world and should be representative of normal driving. The cycle is based on the latest and best knowledge we have on how cars are used in real traffic. Still, this is not sufficient to regulate emissions under all driving conditions and this is why the on-road testing is now introduced in the RDE legislation in Europe. I have not studied how Emission Analytics do but according to the new European RDE testing, a cold start should be included. Unfortunately, there are a number of organizations and companies out there who conduct testing and their results may not always be representative of “real-world” driving. They often highlight some specific driving condition. It is not uncommon that on-road tests are only conducted with warm engines; primary to save time and cost. All-in-all, consumers get misinformed by all the headlines such tests may create. Note that “cold start” usually is defined as a start with cold engine at ~25°C. Cold starts at lower ambient temperatures increase emissions much more than at 25°C. EU regulates this for CO and HC from gasoline cars at -7°C, albeit that the limits are much higher than in the standard test. Cold start emissions of CO and HC are considered much lower from diesel cars and thus, they do not have to be tested. This is based on comprehensive knowledge on results in cold starts in the past. The main problem for cold starts is unregulated emissions that pose health hazard for humans. Gasoline cars are much more affected than diesel cars in this respect (therefore, we want to regulate HC at cold starts). The difference in relative levels can be in the range of 10-100. NOx is generally not a problem during cold starts, since the engine-out NOx is lower (due to lower NO formation) than in a hot start, unless the manufacturer “cheats” in some way. Stopping the engine via conventional start/stop systems or in a hybrid drive is not necessarily “bad” for emissions. This is of particular relevance to consider for engines with low exhaust temperature, such as e.g. lean-burn gasoline engines and diesel engines. At idle, the exhaust temperature might be lower than catalyst light-off temperature and leaving the engine on idle will cool down the catalyst. Stopping the engine gives much lower heat loss and thus, higher catalyst efficiency. You have perhaps noted that there have been several articles on mild/micro hybrid diesel cars that reduce NOx emissions compared to conventional diesel cars on this site. Synergies via hybrid systems can be identified not only regarding higher catalyst temperature but this will be another topic.
@Arnold YES! Electronics always behave as if it was under water. Even under the ice, sometimes. What gives most problems with modern cars? The electrical system! Of course! The more you have, the worse. I know it is contradictory to mention this, since we need hybrid drives in the future on all our cars, but when they introduce this on all their models at once, the queues at the workshops will become long. Now, Audi may have to face similar problems with the electronics that Mercedes and BMW had a couple of years ago. Recall that Mercedes had an electric brake system on their E-class? Failure rate was almost 100%. Of course, the system reverted to the safe and sound electromechanical system in case of failure in the electrical system. For the model after, Mercedes skipped the electric brake system. About all your other comments... Why do you bother to post such crap?