UNITED STATES ENVIRONMENTAL PROTECTION AGENCY



SUBJECT: Impact on Existing Standards  Due to  Proposed  Instru-   DATE: September  18,  1974
         mentation Changes in the Heavy  Duty  FTP
F*ROM*
rKUl-u    William B.  Clemmens

         ^J/M^^-
TO
         Gary W.  Rossow

             Part of the proposed interim changes  in the  heavy duty regulations
         includes changes in instrumentation.   This involves  updating the method
         of measuring unburned hydrocarbons  (HC) for heavy  duty  gasoline engines
         and utilizing a more accurate instrument  for  measuring  oxides of nitrogen
         (NOx) for both heavy duty  gasoline and Diesel engines.

             These new instruments  measure quantities  of  constituents that  the
         present instruments may  or may  not measure due to  their inherent limitations.
         A close look at the correlation between old and  new  instruments is  in order
         such that the impact on  the standards  of  this newer  technology may  be
         assessed.

             In terms of unburned hydrocarbons  from heavy duty gasoline engines
         the present NDIR analyzer  will  be replaced by a  heated  FID which is
         similar to  the unit used in the heavy  duty Diesel  FTP.   This instrument
         measures total carbon in ppm  C  of most forms  of  unburned hydrocarbon
         emitted by  an 1C engine, whereas the NDIR is  more  selective  in the  types
         of hydrocarbons that it  detects.  For  instance,  the  NDIR instrument will
         not detect  HC emissions  of the  Benzene ring type;  and  FID will.  This
         type of ..pollutant occurs in significant quantities in the exhaust of
         gasoline engines and therefore  one can expect the  amount of  HC emissions
         measured by an FID to be greater than  that measured  by  an NDIR analyzer.
         This is indeed the case, and  the current  heavy duty  FTP uses ari-.FID/NDIR
        "volume correction ratio  of 1.8  to account for the  difference.

             New data indicate that this factor underestimates the difference between
         the two instruments.   S.R. Krause 1 ran 168 tests  following  the FTP.  Four
         nine mode cycles were run  on  7  gasoline engines  with a  resultant FID/NDIR
         volume ratio of 2.30 and a standard deviation of 0.14.  Data from South-
         west Research 2 when corrected  for the traditional^FID/NDIR  volume  ratio
         of 1.8 have a mean FID/NDIR ratio of 2.56 and a  standard deviation  of .27
         for 12 tests that were conducted following the 9-mode FTP on 9 different
         gasoline engines.   From  this  information,  the  impact  of  adding the FID
         can be assessed by comparing  the previous correction factor  to the  new
         correction  factor.   Essentially this effectively removes the old correction
         factor from the federal  calculations and  substitutes the new one.   The
         difference  between the factors  is 1.27 to 1.42.  Leaning toward the
         conservative side of the data spread,  because of the fact that S.R. Krause
         had more data,  I recommend the  correction on  a mass  basis (i.e. standards
         are in mass)  of 1.27.  Thus substitution of an FID using the  present FTP.
         calculations for mass of pollutant will give  a 27% higher value than an
         NDIR hydrocarbon analyzer  using the same FTP.
EPA fbirn 1320.6 (fev. 6-72)

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                                 -2-
    Accurate measurements of oxides of nitrogen emissions (NOx) have
always been difficult.  The present NDIR analyzers used in both the heavy
duty gasoline and Diesel FTP measure only NO and not NO + N0£  (NOx).
The NDIR system is very susceptible to interference from water vapor, CO,
C02 and propane.  In addition, the water vapor tends to condense inside
the instrument creating an equipment malfunction.  Therefore, in order to
alleviate the probability of a malfunction, a drier is installed in the
sample line upstream of the instrument.  However, if the dryer is a water
trap a sizeable portion of the N0£ is scrubbed out of the sample.  If the
dryer is a dessicant like "Drierite", the dessicant reacts with the sample
to alter the NO readings.

    More accuracy is available when using a chemiluminescence  (CL) oxides
of nitrogen analyzer, mainly because it is not subject to the interferences
that the NDIR instrument is, and it can be made to measure total NOx with
the addition of a thermal conversion.  The fact that the CL analyzer is
more specific in its detection indicates that the two types of instruments
produce different values.
                                 o
    S.R. Krause in a later paper J assesses the relationship on Diesel
engines with equation (1).  This was the result of 6 engines tested on
a modified 13-mode cycle using SAE instrumentation techniques as required
by the FTP.  A dryer (Aquasorb) upstream of the NO (NDIR) analyzer was
included.  No mention was made of the procedure or hookup of the N02
instrument (NDUV), other than it was used.

    A more thorough study was conducted by Scott Research Labs in conjunc-
tion with TRW Systems Group.  The report ^ included test data from 450
automobiles with gasoline engines as part of the CAPE-13-68 program.  All
tests utilized the 1975 FTP or the Federal Short Cycle test procedure.
The instrumentation (FIG 1) consisted of an NDIR (NO) analyzer with Drierite
and a downstream CL (NO or NOx) analyzer, both parallel to an NDUV (N0£)
analyzer.  Parallel to this group of instruments was still another CL (NOx)
analyzer for cross correlation.

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                                  -3-

    The results indicate that equation  (2) describes the relationship
between CL and NDIR with all interferences for the NDIR instrument
                                                                 •i
present including Drierite.  However, neither Heavy Duty Gasoline nor
Diesel measure NOx in the FTP.  All that is measured is nitric oxide
(NO).  Bag samples from reference ^ indicate the  (NO) relationship  in
equation (3)  between a CL analyzer without drierite and an NDIR in-
strument with drierite.

    Eq (1)  (NOx) NDIR + NDUV = .994 (NOx) CL +75.6 ppm

    Eq (2)  (NOx) NDIR + NDUV = 1.34636 (NOx) CL - 13.43882 ppm

    Eq (3)  (NO) NDIR = 1.12184 (NO) CL + 8.36667 ppm

    This last comparison is probably the most valid approach since  it
compares directly to the instruments in use - an NDIR with drierite
measuring (NO).  However, the expected use of the chemiluminescence
analyzer will be in the (NOx) mode.  Remembering that (NOx) = (NO)  +
(N02)> evaluating the relationship expressed in equation (3) provides
half of the answer.  The relative change in response between NDIR and a
CL in the (NOx) mode should then be the change in response due to
measuring (NO) on the CL compared to the NDIR response plus the  amount
of N02 in a typical sample.

    In general the amount of N02 formed during a typical internal
combustion process can be characterized as 2-5% of the total NOx formed.
This remains fairly true for a raw sample of the combustion products.

    Putting equation (3) into the following form

    (4)  (NO)^T =N°NDIR - 8.36667 ppm
             CL       1.12184

and evaluating this equation (4) for a typical range of NO values which
are presently being measured by NDIR, Table I is constructed.

                                Table I
                                                     Relative
                                                   Response of
ppm (NO)         Calculated                       CL compared to
by NDIR        ppm NO from CL    CL/NDIR (%)         NDIR (%)

  500              438.24           87.64           - 12.35%
 1000              883.93           88.39           - 11.61%
 2000             1775.33           88.76           -11.23%

    Stating once again that NOx = NO + N02 it can also be said that

    (5)  ANOx = ANO + AN02

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                                 -4-

Substituting the relative response of the CL analyzer from Table I as
the change in NO measurement (ANO) and the conservative value of the
previously unmeasured N02 as the change in NC>2 measurement (AN02), the
total effect of substituting a chemiluminescence analyzer operating in
the NOx mode, can be assessed.

    ANOx = A NO +AN02

    ANOx =   -12% + 2%

The net change in NOx measurement is approximately a negative 10%.
The recommended adjustment factor for substitution of the chemiluminescence
system becomes .90 times a standard based on the existing heavy duty FTP.

Bibliography

1.  "Effect of Engine Intake-Air Humidity, Temperature and Pressure on
    Exhaust Emissions," S.R. Krause, Oct. 1971, SAE 710835

2.  Letter from Southwest Research to J. Bascunana (EPA) dated Feb.
    11, 1974.

3.  "Effect of Inlet Air Humidity and Temperature on Diesel Exhaust
    Emissions, " S.R. Krause, January 1973, SAE 730213.

4.  "A study of Mandatory Engine Maintenance for Reducing Vehicle
    Exhaust Emissions," Vol VI, year end report, Scott Research & TRW
    Systems Group, July 1972.

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                                                                                                £}.= EQ//2
                                                                                                g^ EQ//3
                                                                                                   •EQ//1
                 FIG 2
L_
                                           500
                    PPM CL
Correlation Between CL and NDIR, NDUV
                                       1000

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