MEMORANDUM UNITED STATES ENVIRONMENTAL P ROTECTION AGENC Y NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY 2565 PLYMOUTH ROAD A N N ARBOR, MICHIGAN 48105-2 4 98

OFFICE OF AIR AND RADIATION

SUB J EC T : Considerat i o n of Confidential Business Information on the Relationship between Engine-Out NOx Emissions and Fuel Consump tion

FROM:

TO:

DATE: Charles Moulis, Senior Environmental Engineer Assessment and Standards Division

Matt Spears

, Director Heavy-Duty Onroad and Nonroad Cente r

August 3

, 2012

T his memorandum s ummarizes our analysis of the relationship between engine-out NOx emissions and fuel consumption for the 2012 Nonconformance Penalty (NCP) Final Rule, which is also s ummarized in Figure 3-2 of the Final Technical Support Document for that rule.

Engine-Out NOx and Fuel Consumption Data

Before and during the rulemaking to establish NCPs for mod e l year 2012 and later heavy heavyduty diesel engines

, engine manufacturers provided us with information about the relationship between engine-ou t NOx emiss ions and fuel consumption for their heavy heavy-duty engines. Most of this information was identified as confidential business information (CBI) by the manufacturers so we are not releasing it to other manufacturers or anyone e lse. The Clean Air Task Force also provided public data collected by M.J. Bradley. These data are shown togeth e r in Figure A, which plots normalized fuel consumption versus engine-out NOx emissions. Manufacturer data is presented with fuel consumption normalized relativ e to each manufacturer's own compliant 0.20 glhp-hr (tai lpipe) engines.

These data do not fall on a sing le li n e , which is not unexpected since absolute performance can vary significantly from one engine model to another. This can be corrected to some extent by replotting the data so that fuel consumption i s normalized to equal 1.00 at 3 glhp-hr engine-out N consistent with the ·ant · · . This ach is shown in F. B.

second set of dat a from M.J. Bradley is added to the plot. This second set was excluded from the first figure because the data are not from engines compliant with the 2010 NOx standar d

, but rather represen t ed earlier eng ine s.EPA Analysis of Engine-Out NOx and Fuel Consumption Data

To comp l ete the NCP rule

, EPA needed to gene rate a single estimate of the difference in fuel consumption between an engine with e n gi n e-ou t NOx emissions at 3.0 glhp-hr (the est i mated engine-out emissions of a comp liant engine) and an engine with engine-out NOx emissions at 4.8 g/hp-hr (the estimated engine-out emissions of the baselin e engine). To eva l uate other alternative cost scenarios, similar estimates were also needed relative to engines with engine-out NOx emissions at 0.50 and 1.2 g/hp-hr. Therefore, we developed a single curve of relati ve fuel consumption versus engi ne-ou t NOx emissions in the 0.50 to 4.8 g/hp-hr range. This curve is show along with the data in Figures A and B.

Given the limited amount of data available and the inconsistencies betwe en the various sources, it was not possible to d evelo p an appropriate curve by a pur e ly statistical analy s is of the data such as averagi ng the data. Instead

, we subjective ly develop e d the curve based on the following principles:

• Manufacturer data s hould be r oughly weighted based on each manufacturer ' s approximate share of the heavy h eavy-d uty engine market.

• Data provided in the 3 .0 to 4.8 glhp-hr range should be given a greater weight becau se this is the range that represents the expected change in engine-out emiss ion s and resulting fue l consump tion from the baseline engine to a compliant engine. Thus

, this is in the
range used to define the final penalty amount.

• Data provided in more detail should be weighted more highly than data provided in lesser detail.

• The line should be continuous, but curve slightly to r e flect the known trend of flattenin g at high e r NOx levels.

• The projections for NOx levels bel ow 3.0 g/hp-hr shou ld represent fuel co n sumptio n changes ob served and reported fo r 2010 engines relative to 2009 engines.

• The curve should be somewhat conservative to protect complying manufacturers, but not unreasonably conservative. It should be conservative with respect to both the analysis used to set the penalty and the alternative scenarios.

The result was the line shown in the figures which follows the following equation:

Relative Fuel Consumption= 

### 0.0007 x (NOx) 2

- 

### 0.0157 x (NOx) 

### + 1.0408

This curve projects that there would b e a 1.9 percent decrea se in fuel consumption associated with in creasing engine-out NOx emission from 3.0 to 4.8 glhp-hr

, equivalent to a negative s lope of 1.056 percent pe r g/hp-hr. This slope is compared to the slopes of the raw data sets in Figure C. 

### In this Figure, lines lyin g above the EPA line (i.e., lines w ith shallower slopes) r epresent proje ctions of smaller fuel consumption impacts, while lines lying below the E PA line ( i.e

., lines with s t eepe r slopes ) repr ese nt projections of larger fuel consumption impact sAlthough the derivation of this curve was ultimately subjective, it can be evaluated to some degree by the following observations:

• The slope of the curve falls within the range of data for engine

- out NOx levels both above and be l ow 3.0 shown in

• The slope of the curve (as shown in Figures Band C) is conservative (i.e., it projects a slightly high er fuel consumption penalty for relative to the baseline) with to the all data for

• The curve i s relatively straight. However
, it curves very slightly to be steeper for engineout NOx levels below 3.0 glhp-hr and l ess steep for engine-out NOx l evels above 3.0 glhp

- hr. A mor e curved line would have been less conservative by projecting a smaller fuel consumption advantage for the optimized 0.50 glhp

- hr SCR engine used as the base l ine for the penalty (which has engine-out NOx emissions at 4.8 glhp-hr). A more curved line would ha ve also projected a larger fue l consumption disadvantage for a nonSCR 0.50 and 1.2 glhp-hr baseline engines considered in alternative scenar ios

. • The 2.25 per cent differ ence in fue l co n s umption betwee n our ' 3.0 n /

,....,._,..

- ..**t~·** ..**·~~** and an with NOx emissions at 1.2 i s within

This value is significantly lower than the values reported by SCR engine manufacturers in their marketing material s, but those marketin g values are generally assumed to reflect be st -ca se engine operating sce narios.

• The curve r esu lt s in a reasonable 1.1 percent change for reducing emissions from 1.2 to 0.50 glhp-hr.

Thus

, we concluded that this curve was mo st consiste nt with the available data and the guiding principles described above.

Comparison to Tailpipe NOx Estimates

As is described in the F inal Technical Support Document, combining this curve with our estimates of catalyst efficiency, we project that the fuel consumption for an SCR engine optimized for 0.50 g/hp

- hr NOx would be 1.9 percent better than an SCR engine optimized for 0.20 g/ hp-hr NOx. This compares very well w ith the public comments of the Clean Air Task Force
, Cummins

, and Mack

, each of whom est im ated that there would be a two percent difference in fuel co n sumption between the 0.20 and 0

. 50 g!hp-hr SCR engines.On t h e ot h er ha n d, our esti m ate is m uch l ower t h a n t he four percent value recommen d ed by P ACCAR

. There are several reasons why we believe this is appropr i ate. First, the relevant compliance costs are those representing the 90th percent il e costs. Since PAC C AR currently represents less than te n percent of the hea vy heavy-duty engine market and it was the on l y manufacturer to report a fue l consump t ion impact above two percent, we can co nclude that it is that the 90th would be l ess than the value P ACCAR.

C onclusion

EPA analyzed the relevant data to estimate the r elat i onsh i p between engine-out NOx emissions and fuel consumption for heavy heavy-duty engines. The resulting curve is cons i stent with the available data and the guiding princip l es l isted above. Thus

, it is appropriate for the NCP Final Ru l e. This curve was used in that Final Rule primari l y to estimate the differe n ce in fuel consumption between an engi n e wit h engine-out NOx emiss i ons at 3.0 glhp-hr and an e n gine with engine

- out NOx emissions at 4.8 glhp

- hr (which was used as an i n put to the cost ana l ysis)

, but also to evaluate other alternative cost sce narios. The projection that the fuel consumption for

an SCR engine op t imized for 0.50 glhp-hr NOx wou l d be 1.9 percent better than an SCR engine optimized for 0.20 glhp-hr NOx compare s very well with the public comments of the Clean Air Task Force, Cumm i ns , and Mack, each of whom estimated that there would be a two percent d i fference in fue l co n sumption between the 0.20 an d 0.50 g/hp-hr SCR eng i nes.1.041.031.02c01.01E:s1.008Qi:sLL.0.99Ql>nJQi0.98ac:0.970.96IIIIIIFi!!ureA-DataNormalizedRelativetoComoliantConfigurationsFuelConsumptionvs.EngineOutNOxEmissionsContainsConfidentialBusinessInformationREDACTEDIIIII_jL0.95012345678EngineOutNOX(g/hp-hr)FigureB-DataRenormalizedRelativeto3g/hp-hrFuelConsumptionvs.EngineOutNOxEmissionsContainsConfidentialBusinessInformation1.04c:0E1.031.021.01c:0uQju..1.00cu>cucr:::0.990.980.97-!=========J:=========t==========t==========J=========t==========F========F=======!0.01.02.03.04.05.06.07.08.0EngineOutNOX(g/hp-hr)FigureC-FuelConsumptionRelativetoNOxIncrementFuelConsumptionvs.DeltaEngineOutNOxEmissionsContainsConfidentialBusinessInformation1.011.00c00.99"iE:JIllc00.98Ql:JLL.Ql>+i(Q"ii0.970.960.950.00.51.01.52.02.53.03.54.04.55.0DeltaEngineOutNOX(g/hp-hr)