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Peter_XX
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We know that H2 storage and transport is very expensive and consumes a lot of energy. Regarding current and near-future production capacity, it is clear that any "green" H2 produced today could be utilized in refineries. I have not looked at any studies of efficiency of use in each case, but I would guess that the refinery route would be more efficient than using “pure” H2. In contrast, however, the use of pure H2 gives better PR and headlines. With current legislation and incentives refineries would not get full credit for using green H2. Another prohibitive factor is the cost of green H2. The PREEM refinery in Sweden just recently ditched an investment of upgrading heavy oils to fuels. This is said to be due to “commercial reasons”, but also public opinion played a part. The project would have significantly increased CO2 emissions in Sweden. However, when I last time I checked, it seemed as if CO2 emissions was a global problem... By the end of the day, of course, another refinery in another part of the world will make necessary investments to do this job. Probably with lower environmental constraints and higher CO2. Sad. I should point out that PREEM currently make H2 from NG. Needless to say, “green” H2 is prohibitively expensive.
I am glad to see that Carl brought up the NOx/VOC problem. I would also say that EPA's statement that "NOx reductions can actually increase local ozone under certain circumstances..." is somewhat prudent. This is rather rule than exception, i.e. ozone formation is limited by VOC in close to 100% of all cases (in densely populated areas). This is, for example, manifested in the "weekend ozone" paradox that we see in most cities (also in Europe). Ozone is higher during weekends when heavy-duty traffic is limited. This means that further reduction of NOx from heavy-duty vehicles might actually increase ozone levels. Besides that, reduction of NOx will provide positive health effects, so in general, tighter emission limits on NOx is positive, particularly if also VOC (mainly from light-duty) traffic could be reduced simultaneously. There is, however, most likely a threshold effect when there is no positive impact of further reductions of NOx. Note that the lung itself produces NO (you exhale it). Moreover, NO is a natural compound in the body that has several positive health effects, for example, vascular dilatation, which reduces blood pressure. NO is also first defense against pathogens. Sun exposure and ingestion of nitrates, e.g. from vegetables (for example beet root juice, frequently used in sports), are sources of NO in the body. In contrast, there seems to be no threshold level for particulates. Here, a lower level is always better.
Hydrogen is also needed to produce diesel fuel; in some cases, even more than for producing gasoline. Hydrocracking of heavy components to make diesel fuel and jet fuel is a specialty of Swedish refineries. A large expansion is in progress, provided that a permission is granted by authorities and the Swedish Government. Hydrogenation of biocomponents to enable blending in diesel and gasoline fuels is also part of the concept and this will further increase the need for hydrogen. Use of fossil-free hydrogen as a substitute for hydrogen from NG would be complimentary to blending biofuels into gasoline or diesel fuel. The real problem is to produce hydrogen from non-fossil sources in an affordable way. Currently, fossil-free hydrogen is far too expensive.
It continuously surprises me that the VW group always seems to pair the "old" 1.4-liter TSI engine with plug-in hybrid drivelines and not the modern 1.5-liter TSI engine with Miller System (or the VW denotation for it, if you prefer...). The 1.5 engine has higher efficiency, particularly at high loads, and with hybrid drive, you tend to run the engine at a higher load to gain efficiency. Moreover, a larger engine size normally leads to lower efficiency on low load, due to increased friction losses, but this is particularly what a hybrid drive tries to avoid, as indicated above. It is as if you would say that VW tries to avoid the optimal solution. I would love to hear their comments on this.
Some short comments are (I can provide more if anyone is interested…): The e-machine significantly increases the inertia compared to a conventional turbo. Therefore, considerable power is needed just to maintain equal transient response compared to a conventional turbo. Of course, even higher power will improve response and for that, you need a 48 V system. In essence, this is why we have not seen the e-turbo in production so far. Boost pressure at low engine rpm is limited by pumping of the compressor and that potential is more or less exploited already today. Probably the biggest gain might be engine power at high rpm; for sure an important feature for AMG. A bigger turbine than a conventional turbocharger will not choke and reduces backpressure at high engine speed. This facilitates higher power, although boost pressure is not much affected. Will the gain be worth the effort? Well, let’s see if anybody else will adopt the e-turbo... It looks expensive but this is the case also for twin-turbo, e-compressor, and some other options.
To give an example: Twin-dosing of urea reduces NOx by approximately 80% on passenger cars.
@The Lurking Jerk & Michael Some parts of this concept are already in production on passenger cars. I suppose this answers most of your questions/concerns.
Then, the efficiency should be higher than 45% since this can be achieved in a rather conventional diesel engine running on ethanol. Moreover, a practical hydrogen fuel cell seems to be limited to about 60%. This should also be compared to a level of up to 55%, which seems feasible with an advanced diesel cycle and compound turbine in a not so distant future. Options, or extensions to turbo compounding, could be a rankine bottoming cycle, dissociation of ethanol, or a more advanced combustion cycle (e.g. something like HCCI). A fuel cell has "cool" exhaust and no option for recovering waste energy. It is not as if a fuel cell, per definition, would be superior. Moreover, it is not easy to aim at a moving target. Nevertheless, the use of alcohol fuels in fuel cells would overcome the problems in the distribution and storage of hydrogen. This is, more or less, a show-stopper today.
@SJC_1 Yeah, but only if efficiency is high (preferably approaching 96%); not around 30%. I see no information about efficiency (?). The case for the direct methanol fuel cell is similar. Interesting, but not feasible at current efficiency levels.
All right, here we have better info: https://www.motortrend.com/news/duramax-ddsf-cylinder-deactivation-chevy-silverado-gmc-sierra/
I found this quote after a quick search: "There are many similarities,” Bailey said. “Whether it’s a gasoline, spark-ignited engine or compression-ignited engine, you have to modify the valvetrain. So we need the capability to deactivate cylinders on an individual basis." https://www.freightwaves.com/news/cummins-testing-cylinder-skipping-to-reduce-nox-emissions
@sd I am almost 100% sure that they must control the valves. Otherwise, a significant increase in exhaust temperature (and FC reduction) would not be possible. Perhaps someone who has looked at the paper could comment. If it would have been so easy as just to modulate injection, we would have seen this long ago. This technology should have a bigger potential on LD engines.
Gasoline vs. diesel (with similar transmissions): Power: 150 PS vs. 150 PS FC: 4.7 – 4.9 l/100 km for gasoline and 3.6-3.9 for diesel CO2: 117-132 g/km for gasoline and 96-101 g/km for diesel Now we can see why most focus in engine development is on gasoline today. There is some homework to do in this field...
It is nice to see that suppliers have taken on this challenge but I would say "too little and too late" to have any significant impact.
The e-cat has been around for quite some time but has only been in limited production in some case over the years. Perhaps this could lead to a breakthrough.
You can only sell a limited number of cars to "green addicts". https://insideevs.com/news/402234/carlos-tavares-selling-evs-to-green-addicts/
I think there are two main take-home messages from this study: 1) There are many other sources of particle emissions than the tailpipes and 2) This field should be studied in much more detail before conclusions are made. For sure, we already knew about that there were such gaps in the knowledge.
Volvo says 7 g/km in WLTP. This is far less than 7%. If baseline is 200 g/km (?), it would be only 3.5%. Then they also say: “…up to 15% fuel savings” but that is most likely under ideal conditions and it would be far lower under “normal” real-world driving conditions. Still, if the general powertrain development gives approximately 0,5% per year in improvement, it would still be a substantial gain. @Alain Car manufacturers will make a fortune on customers like you. Early adopters always pay a lot for their curiosity.
I just saw a note that Toyota has stopped selling new Prius cars in Sweden. Not any interested customers, as it seems.
@Brian I would say that a 3-liter engine actually provides too much power for this kind of vehicle. Moreover, state-of-the-art for a new twin-turbo 2-liter engine is around 250 hp and with some additional electrical power, you could come pretty close to the performance of a 6-cylinder engine. Regarding NOx emissions, I would guess that this concept should be able to get >90% reduction of NOx in comparison to the Euro 6d (final) RDE limit. Actually, some BMW cars have already showed even lower levels in on-road emissions tests.
When you talk about piston engines and aircraft, consider this concept: A combination of a diesel engine, as the Napier Nomad concept but more up-to-date, and further development of the propfan could work. It would be more fuel-efficient than current jet engines and offset the higher engine weight by the carrying less fuel. However, problems such as, e.g., noise and the relatively low cost of jet fuel today are probably prohibitive. The point is that a piston engine propelled aircraft could perhaps be brought up to modern standards, without too much sacrifice of speed and altitude in the flight. Problems might lie in lack of know-how by jet engine manufacturers for both mentioned technologies and the willingness to allocate resources for such a project. Recall that Junkers Jumo 205-208 was an aircraft diesel engine superior in many aspects to aircraft gasoline engines during WWII. Similar concepts have been proposed in recent time, but instead, I would like to highlight the advancements of Achates, as an example for technology based on a similar concept. Germany lost WWI and much know-how was lost, jet engines came along, cheap jet fuel was available, and Napier did not have the resources to develop their concept further. https://en.wikipedia.org/wiki/Napier_Nomad https://en.wikipedia.org/wiki/Propfan http://achatespower.com/