2007 Diesel Smog Standards - Power vs. Emissions

Scott Harrison

"Growing old is mandatory, growing up is optional"
Staff member
Contributing Member
From Diesel Power Magazine 9/06:

2007 Diesel Smog Standards - Power vs. Emissions
When the roll-out of Ultra Low Sulfur Diesel (ULSD) began on June 1, 2006, it signaled a sea change in the diesel engine emissions environment. Before you jump to the conclusion of "it's the end of easy power mods for diesel engines," we've got some surprising observations, recommendations, and speculation from industry insiders on how we'll still be able to enhance the power output of our machines after January 1, 2007.

But first, since ULSD is a key component in reducing polluting emissions from all road-going diesels, here's a quick overview of what it is and how it'll affect your engine. The EPA is requiring refiners and fuel importers to cut the sulfur content of highway diesel fuel 97 percent, from 500 parts per million to 15 ppm. The switch to ULSD fuel is scheduled to be complete this fall in California and by late 2007 for the rest of the nation.

According to the plan, owners of '07-and-later model year diesel-powered highway vehicles must refuel only with ULSD fuel. If you own an '06-and-earlier diesel, you can fill with ULSD or Low Sulfur Diesel fuel during the transition period. December 1, 2010, is the planned date to complete the transition, and only ULSD fuel will be available for highway use from that date forward.

For the most part, power and performance shouldn't suffer with the new fuel, but fuel economy is expected to be lower because the process that removes sulfur can reduce the energy density of the fuel. That, of course, lowers the miles per gallon. Expect about a one percent loss across the board.

The new fuel will have lubricity and stability additives mixed in at the refineries, making the fuel compatible with older engines. Those engines will have a bit more flexibility in that they can burn the new fuel as well as the earlier blends if necessary. The newer engines cannot.

How The New Regulations Impact The Diesel Power Aftermarket ULSD allows several layers of emissions technology for diesels. Additional catalytic converters, particulate filters and aftertreatment components (that the sulfur would have destroyed) are on the way.

To find out how this will affect diesel performance, we talked to several industry sources and even had a terse conversation with the spokesman from the California Air Resource Board (CARB). Here's what we learned about the situation regarding installing aftermarket parts and tuning diesels for performance. The OE engine manufacturers have to meet federal and state-mandated standards. These are different than for gasoline vehicles but include many of same elements. The difference between diesel and gas engine emissions standard is mainly found in the control of particulates and nitrogen oxides. Unburned hydrocarbons, carbon monoxide, and carbon dioxide are close to the same as gas spark-ignition engines.

What Makes Modification Emissions Legal?
As most readers are probably aware, the aftermarket has worked with CARB to design an approval process for California street-legal, emissions-compliant components. If an installed component doesn't negatively affect the vehicle's emissions, it may be granted a CARB executive order. However, since 2001 there's been a disconnect in the ability of the aftermarket to get diesel performance products approved and get an executive order issued because CARB simply hasn't been awarding them.

In talking with the staff at Banks Engineering, they said that as far as they understand it, CARB is developing a new form of tests that would more properly capture the emissions of diesel engines. So what it comes down to is that since there is no test procedure for diesel in place right now, CARB is very wary of giving diesel products an executive order. Until this test regimen is implemented, the aftermarket companies are sort of in limbo, as is the diesel performance enthusiast.

For aftermarket firms, this becomes a very gray area in terms of aftermarket sales of emissions-legal products for diesel engines. You have to keep in mind that the facts are time sensitive, and as soon as CARB announces its test regimen, whatever we say here will probably have to be amended.

Diesel Emissions Equipment-Today
Diesel catalytic converters were introduced in the mid 1990s, and exhaust gas recirculation (EGR) systems started showing up on most diesels introduced in the late 1990s. Presently, those are the only emissions systems that are required to make the engine run.

Currently, we're not aware of any states that are "sniffing" the exhaust of diesel engines to check emissions compliance for hydrocarbons, nitrogen oxides, and carbon monoxide. There are a few with visual inspections to check that required components-such as the catalytic converter and EGR-are installed and working properly, as well as a few that run opacity tests to verify soot levels.

Part of the reason for this lax enforcement effort is that the equipment to conduct a diesel vehicle emissions test is very expensive, and the program would be very costly. As the CARB source told us, the diesel fleet is such a small percentage that the agency believes that the effort wouldn't be cost effective. However, the source also said that in California the Bureau of Automotive Repair runs the inspection programs, and any future program would originate from that agency.

Diesel Emissions Equipment-2007
Much of the strategy to reduce diesel emissions in the future will be accomplished by reducing the amount of sulfur in the fuel. The new cleaner fuel enables more efficient catalytic oxidizers, particulate filters, and chemical aftertreatment of exhaust to take out the nitrogen oxides. In addition, controlling the engine's output, injection quantity and timing, and EGR will be part of the emissions control package.

We know that the long-range hope of CARB is the advancement of onboard vehicle diagnostics to a level that is so bulletproof you can't remove systems or defeat them. That way, a smog inspection would entail just plugging the scanner into the OBD II port under the dash. Keep in mind that these measures are probably about five years away from being implemented.

Will Future Emissions Controls Hinder Performance?
Technically, there's no reason it should, but the politics might. The emissions equipment and tuning is scalable, meaning that the aftertreatment components for heavy-duty, high-powered applications are already designed. It's a matter of adapting these components appropriately to meet the performance desires and the emissions requirements.

Consider that in the certification process the engines are tested on a dyno, and the chemical emissions are rated in grams per horsepower/hour, which, of course, relates back to grams per mile. This allows scaling the emissions control to meet the need for higher-output, high-torque, high-power engines to do heavy- duty work. The hardest emissions to control in diesel are nitrogen oxides, but with the urea injection and SCR technologies, this should not be an issue.

Again, it's a matter of scaling the technology to fit the mass flows and power output. Will the regulatory agencies provide a channel to test and prove that aftermarket products meet the requirements? Until that question is answered, everyone will be in limbo. In the future, Banks Engineering predicts a complete diesel performance package will likely need to add high-flow particulate filters and catalysts, as well as enhanced urea injection programming.

Does Clean = No Power?
Because of the open-ended nature of the problem, we thought some guidance was in order, and we decided to pass along the following observation from Banks Engineering: they never recommend the removal of emissions products.

In most cases, says a source from Banks, "The times we've tested and tuned with and without catalytic converters, we haven't noticed that much difference in performance. We measure exhaust backpressure and multiple points in the exhaust system, and it is rare that the catalytic converter is a restriction. So in terms of performance, the cost of compromising the current emissions systems and the vehicle warranty don't justify removing the catalyst for a street performance system."

Emission Control Systems

Diesel Particulate Filters
There are several types of particulate filters on the market and being used in Europe. They haven't been instituted in the U.S. yet, mainly because the diesel fleet in the U.S. is a fraction of the size it is in Europe, where over half the fleet is diesel powered. But they're coming, so we'll talk about them briefly. Basically, most designs use a ceramic matrix somewhat like the familiar gasoline-engine catalytic converter. They catch the particulate mass in the matrix and then burn it off to regenerate (or unclog) the filter.

Oxidizing catalytic converters
These are chemical reactors that convert a portion of the chemical emissions mix-unburnt hydrocarbons and carbon monoxide-from the combustion of fuel into different chemicals that are deemed benign.

Selective catalytic reduction (SCR)
This technology neutralizes nitrogen oxide emissions by chemical reaction. Basically, the systems use urea dissolved in water then injected into the exhaust stream. The urea changes to carbon dioxide and ammonia. The ammonia then reduces the nitrogen oxides in the selective catalytic converter, producing water and nitrogen. This is the technology, or some variant of it, in DaimlerChrysler's Bluetec clean diesel technology.

Ultra Low Sulfur Diesel fuel
Removing sulfur from diesel fuel reduces acid rain by allowing catalysts to work without clogging. Using particular filters is dependent on low sulfur fuels as well.

Injection/engine management
By controlling injection pressure, timing, and fuel quantity, we can control nitrogen oxides and particulates. This is one of the main benefits along with great power and efficiency of the modern common rail direct-injection diesels. We've discussed most of the issues regarding soot formation and injecting fuel to burn most effectively with little left over to heat the exhaust system. For example, retarding injection timing is known to reduce nitrogen oxide formation but also increases EGT and reduces fuel mileage. It can also increase the amount of unburnt hydrocarbons in the exhaust gas, requiring more aftertreatment with catalysts.

2007 Diesel Emissions Egr Diagram

Exhaust gas recirculation
EGR is one of the more useful techniques for reducing nitrogen oxide emissions. Diesel exhaust consists mainly of carbon monoxide, nitrogen oxides, and good ol' H2O. Recirculating a portion of the exhaust gas dilutes the intake charge mixture and reduces the O2 concentration.

There are three ways EGR is thought to reduce nitrogen oxide formation. It seems that the dilution of the intake charge increases ignition delay, and, therefore, has the same effect as retarding the injection timing. It also seems that EGR-diluted air mixture reduces the flame temperature, which reduces combustion chamber temperature. It's also thought that the addition of the inert EGR gas in the intake increases the heat capacity (specific heat) of the non-reacting elements present during combustion. The increased heat capacity has the effect of lowering the peak combustion temperature.

Tuning the amount of EGR centers on balancing the trade-off between reducing nitrogen oxides and increasing soot, carbon monoxide, and hydrocarbons. We know a lot about the effects of EGR in diesels, so it's simply a matter of designing the sensors and actuators that can actively and accurately control EGR percentages in relation to engine load conditions. After about 50 percent load, EGR particulate emissions increase significantly and other measures, such as a particulate trap, need to be employed.

Diesel Emissions That Are Regulated

These chemicals are limited to a specified gram per mile output. We didn't put the values because it's just dizzying and ridiculous to list them. If you want to find out more, see the CARB or EPA Web sites. But be warned, your eyes will just glaze over. It's so Byzantine that even the factories with their armies of lawyers are paying billions of dollars in fines for non-compliance.

A final observation on this subject. It's interesting that Tier 2 monitored emissions switches from unburned hydrocarbons to NMOGs and HCHO, which are emission elements from ethanol in gasoline.
100 % Bio-diesel. Smelled bad too :buck2: They had normal diesel also, but the line at that pump was crowded, so I figured "what the heck". Next time I'll wait in line. I was pulling the trailer and didn't really see any difference in performance.



Aloha everyone.
interesting read. thanks for the info Scott.

FWIW we have used B20 and noticed an improvement in mileage in both our Detroit and the ISB 24V Cummins.

I am seriously considering setting up a WVO system on the Cummins.

Bio diesel is supposed to clean out any loose perticulates in your petro diesel system. If you are using alot of bio be sure to change your fuel filter more regularly early in the transition process. It has been said that many motors will run quieter and even run more efficiently.

It will be interesting to see how the changes over the next few years effect the diesel performance aftermarket.