Ricardo Achieves Tier 2 Bin 5 Diesel Emissions Without NOx Aftertreatment; Tracking to Tier 2 Bin 2
12 September 2007
Ricardo has achieved Tier 2 Bin 5 emissions from an automotive diesel engine without the use of NOx aftertreatment. This research continues with the aim of demonstrating clean diesel technology capable of achieving Super Ultra-Low Emission Vehicle (SULEV) and Tier 2 Bin 2 requirements. (Earlier post.)
Ricardo’s ACTION (Advanced Combustion Technology to Improve engine-Out NOx) research is delivering reduced engine-out emissions through the application of Highly Premixed Cool Combustion (HPCC). NOx reduction is primarily achieved through the reduction of charge oxygen concentration, accomplished by reducing the air/fuel ratio and increasing exhaust gas recirculation. Technologies involved include advanced air handling systems, two-stage series-sequential turbocharging, advanced exhaust gas recirculation, and application of closed-loop cylinder pressure-based engine controls.
Ricardo achieves HPCC by injecting fuel during the ignition delay period, as opposed to the early injection of other HCCI-like schemes for low temperature combustion and reduced NOx. HPCC results in very low NOx and soot emissions, with moderate increases in HC and CO emissions.
In parallel, Ricardo developed an advanced exhaust aftertreatment system which combines a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF). When combined with HPCC and engine optimization, this has delivered Tier 2 Bin 5 emission levels without NOx aftertreatment. Further research has established the feasibility of adding a lean NOx trap (LNT) into the system.
Through simulation and test results, early predictions indicate that the diesel will be capable of meeting the requirements of SULEV/Tier 2 Bin 2 emissions standards, thereby achieving NOx levels less than one-tenth of the Euro 5 levels.
| Tier 2 Emission Standards, Bins 5 and Below, g/mi | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Bin# | 50,000 miles (Intermediate life) | 120,000 miles (Full life) | ||||||||
| NMOG | CO | NOx | PM | HCHO | NMOG | CO | NOx* | PM | HCHO | |
| * Average manufacturer fleet NOx standard is 0.07 g/mi | ||||||||||
| 5 | 0.075 | 3.4 | 0.05 | - | 0.015 | 0.090 | 4.2 | 0.07 | 0.01 | 0.018 |
| 4 | - | - | - | - | - | 0.070 | 2.1 | 0.04 | 0.01 | 0.011 |
| 3 | - | - | - | - | - | 0.055 | 2.1 | 0.03 | 0.01 | 0.011 |
| 2 | - | - | - | - | - | 0.010 | 2.1 | 0.02 | 0.01 | 0.004 |
| 1 | - | - | - | - | - | 0.000 | 0.0 | 0.00 | 0.00 | 0.000 |
Throughout the project, a major emphasis has been placed on achieving low emissions under transient conditions to maintain or improve the fun to drive responsiveness of the engine without deteriorating emissions performance. The engine has been developed with a competitive power rating of 65 kW/liter to meet US emissions regulations for both sea level and altitude compliance.
Having demonstrated these accomplishments on the test bed, the powertrain has now been installed in a test vehicle to enable calibration refinement and validation. In the coming months Ricardo intends to carry out extensive vehicle testing to validate the achievement of SULEV/Tier 2 Bin 2, currently the world’s cleanest emissions standard. In doing so, the research team aims to maintain or improve engine responsiveness and customer appeal, while also delivering a significant fuel economy and CO2 improvement over current US equivalent gasoline engines.
The achievement of Tier 2 Bin 5 engine-out emissions without NOx aftertreatment is a major breakthrough and puts us squarely on the path to achieving our ultimate objective of Tier II Bin 2, the world’s cleanest emissions standard. While there clearly remain many challenges in translating this research into high volume production solutions, this achievement provides significant new confidence in the future viability of the clean diesel in North America.
—Dean Harlow, president of Ricardo, Inc.
Resources:
“Advanced Diesel Technology to Achieve Tier 2 Bin 5 Emissions Compliance in US Light-Duty Diesel Applications”, SAE 2006-01-1145 (Ricardo)
I guess US legislators really didn't think anyone could pull this off for the NOx? My hats go off to the engineers that are doing this amazing work... question is, if everyone in the US starts driving vehicles that consume a third less fuel, how is the government going to get a third more tax... time to think of another ridiculous emission limit i suppose?
Posted by: kai | 12 September 2007 at 07:19 AM
kai,
False problem. It is very easy to 2x, 3x, 4x or even 10x fuel taxes on fossil fuels to maintain high retail price and the same (tax) revenues while keeping taxes low on cleaner energy sources.
Looked what happened to taxes on alcohol, presently at 85% + of the total price in many places and people or still drinking.
Posted by: Harvey D | 12 September 2007 at 07:40 AM
So, essentially what they're doing is running the diesel engine less-lean?
Posted by: | 12 September 2007 at 08:13 AM
@kai:
Nowhere in the article any numbers about CO2 emissions are mentioned. On what basis are you assuming the 1/3 of CO2 emissions?
Typically, diesel engines emit significantly more CO2 when compared on a mpg basis with gasoline engines.
The diesel combustion cycle used to be more efficient, as the temperature and pressure differentials were higher compared to a gasoline engine; With EGR, the temperature differential diminishes; with any kind of exhaust aftertreatment, the pressure differential diminishes. Or, in other words, diesel engines used to trade (CO2) efficiency for smog exhausts and vice versa. The cleaner your diesel get, the less the CO2 benefits compared to a gasoline engine. With three aftertreatment systems (DOC, DPF and LNT) required to achive similar exhaust ratings as current (large-scale) production gasoline engines, the CO2 benefit will most likely be equalized, or even turn towards gasoline engines.
Diesel engines have to have at least 15% better mpg numbers to be equivalent to gasoline; here in europe, the CO2 exhausts are getting very equal - and the smog related emissions requirements are nowhere near to be equal for diesels...
The only benefit a larger proportion of diesel on the US market would have, would probably a less steep increase in fuel prices here in europe (as US refineries can then provide a bit more of domestic refined fuel for US cars, and the european markets (Rotterdam) won't be depleted of gasoline as currently the case...
Selfish as I am, that'll be a good thing (stabilizing EU fuel costs for some time at 8-10 USD/gal at the pump).
@Harvey D: as you already mentioned, even with the above price for fuel, no too significant steering effect of personal transport choices is achived. It's reasonable, that the same will hold true also in the US. Nevertheless, I believe the EU is more able to cope with even higher fuel prices than the US, due to the better availability of public transport, water/river channel systems and proximity of industrial centers...
Posted by: realarms | 12 September 2007 at 08:16 AM
With more recirculation the mix would be leaner. This engine would be a dog in hot weather and EGR cleaning would be every 10k. I'll take a pass.
Posted by: Joseph | 12 September 2007 at 11:36 AM
Through simulation and test results, early predictions indicate that the diesel will be capable of meeting the requirements of SULEV/Tier 2 Bin 2 emissions standards
Impressive!
Posted by: jack | 12 September 2007 at 12:30 PM
Looks like major break-through.
Ricardo technology assures total control over timing of ignition event. Pressure wave from ignition of small pilot injection triggers autoignition and cold combustion of major injection (homogenously distributing fuel cloud during ignition delay of pilot injection).
Much less risk of misfire, detonation, or ignition at wrong crank angle with loss of efficiency.
Posted by: Andrey | 12 September 2007 at 10:06 PM
Joseph: EGR systems include filters now - intake cleaning will be a thing of the past.
As to running more rich - not necessarily. This process (HPCC), I believe, basically just allows more time for the fuel to mix under certain low-load conditions, and happens later in the piston's movement. More homogenous fuel-air mix means cleaner burn and conditions also result in less NOx. I believe fuel air ratio isnt too much impacted. I might be wrong.
Realarms: Diesels, even with all the aftertreatment, will still have no problem exceeding 15% better mpg by a large margin. Aside from the differences in CO2 content of fuel, C02 emission is basically directly tied to economy, and diesels will never relinquish their economy advantage to gassers, even heavily optimized lean/FSI spark ignition engines.
Posted by: joeblow | 12 September 2007 at 10:13 PM
@ Mike Millikin -
the ignition delay period is a consequence of the fact that certain precursor reactions in the oxidation chain of long paraffins are endothermic. This slows down the others, which are mildly exothermic. The delay is therefore intrinsic to gasoil fuel, biodiesel, xTL etc. (not DME) and always occurs after the start of injection. Ignition delay is also the reason for the RPM ceiling characteristic of CI engines.
In conventional CI, this delay gives more of the fuel time to evaporate and mix with the fresh charge prior to ignition, which is characterized by the onset of the highly exothermic reactions that follow (blue hydrogen flame, followed by yellow diffusion flame).
HPCC and other variations on late-injection diesel HCCI inject all of the fuel in one quick burst into a mixture with high density and specific heat but reduced oxygen (compared to air). This is achieved via substantial amounts (30-50%) of externally cooled EGR and results in much increased ignition delay. Hence, the fuel has enough time to evaporate completely and form a reasonably homogenous mixture with the fresh charge. This is how PM emsission are avoided. The mixture then ignites spontaneously at many locations almost at once, resulting in nearly complete combustion without a flame front. This is how NOx formation is avoided.
The net result is similar to gasoline CAI (cp. e.g. Mercedes' DiesOtto prototype), but the implementation is very different: gasoline is hard to ignite and CAI therefore requires carefully controlled retained or rebreathed hot EGR to avoid a misfire. Diesel is easy to ignite and therefore requries externally cooled EGR to prevent a flame front forming prior to mixture homogenization.
All of these flameless combustion strategies suffer from increased engine-out HC and CO emissions, but those are easily cleaned up by the anyhow present two-way oxidation catalyst. The fuel economy penalty is overcompensated by the harder (i.e. approximately isochoric and therefore loud) combustion in part load.
@ realarms -
diesel fuel does have 12% higher density than gasoline, so burning a gallon of diesel will produce ~12% more CO2. The point is, diesel engines are so much more efficient in part load compared to *conventional* spark ignition engines that they get at 20-30% further on a gallon of fuel. For each mile, a diesel-powered vehicle will therefore emit less CO2 than the same model with a comparably powerful gasoline engine.
Posted by: Rafael Seidl | 13 September 2007 at 11:08 AM