Effect of Gasoline Fuel Additives on Combustion and Engine Performance

2.1.7
 
Measuring Effectiveness of Additives 
An overview of measurement techniques for additive effectiveness can be seen 
in Table 2.1. No defined method for CF additives exists. However, as mentioned in 
previous sections, the typical chemistry, irrespective of the additive used in 
conjunction, remains similar. As such it can be assumed that reasonable solubility 
from all chemistries can be expected and most appropriate method of testing is trial 
and error. 
FM performance is most commonly assessed by the High Frequency 
Reciprocating Rig (HFFR). A ball is oscillated against a metal plate while submerged 
in fuel. The diameter of the wear mark on the ball from the contact under a 2 N load 
at 60 °C is then measured and used to characterise the lubricating properties of the fuel 
[101]. In Europe, the maximum diameter of the wear scar on the ball from an EU 
standards EN590 diesel fuel is 460 μm. 
CI characteristics are evaluated against the fuels cetane or octane numbers in 
diesel and gasoline fuels, respectively. As described in Section 2.1.2, octane number 
is a measure of the fuel’s resistance to knock under high pressure and temperature 
conditions in spark ignition engines. Test fuel knock-resistance is compared to that of 
a blend of reference fuels isooctane (octane number 100) and n-heptane (octane 
number 0). Octane number found in such way is referred to as Research Octane 
Number (RON).

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2.1 Fuel Additive Review 
41 
Te
st M
ethod
HFF
R
Oc
tane
numbe
r in ga
soli
ne
fue
ls 
and c
etan
e number
a
nd the ignit
ion 
de
lay in diese
l fue
ls
- 
Me
asure
ment o
f e
le
ctric
al 
conduc
ti
vit
y
Me
asure
ment o
f inje
ctor 
flow
cha
ra
cter
ist
ics, w
eight
of intake
va
lves
Me
asure
ment o
f f
ue
l flo
w r
ate
in 
oil
li
ne
s, pum
ping pre
ssure
re
quire
ments
Tr
ea
t R
ate 
(ppm)
25 
- 
1,000
100 
- 
1,000
50 
- 
2,000
1 
- 
40
100 
- 
1,000
10 
- 
50
F
unc
ti
on
R
educ
e fr
ic
ti
ona
l l
osses in fue
l sys
tems a
nd 
im
prove
ope
ra
ti
ona
l l
ife
of f
ue
l sys
tem c
omponen
ts 
in gasoli
ne
a
nd diese
l fue
ls
Impr
ove
c
ombus
ti
on c
ha
ra
cte
risti
cs of ga
soli
ne
a
n
d 
diese
l fue
ls
Tr
ansport f
ue
l non
-solub
le a
ddit
ives in di
ese
l and 
ga
soli
ne
fue
ls
R
educ
e static c
h
arge
buil
d
-up by im
proving 
elec
tric
al conduc
ti
vit
y of
diese
l and ga
soli
ne
fu
els
R
educ
e a
nd p
re
ve
nt 
ca
rb
on a
nd other
de
posi
t bui
ld
-
up i
n fue
l sys
tems
Use
d in pi
pe
li
ne
s to re
du
ce
fr
ic
ti
ona
l pre
ssur
e 
loss
es
Additi
ve
F
ric
ti
on Modi
fie
r 
C
ombus
ti
on 
Impr
ove
r 
C
arr
ier
F
lui
d
Anti
-S
tatic 
Additi
ve
De
posi
t C
ontrol 
Additi
ve
Dr
ag r
educ
ing 
Age
nt
 
Table 2.1: Fuel additive types with characteristic usage and testing information

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2.2 Fuel Metering Systems 
42 
Cetane number relates to a fuel’s ignition quality in mainly compression 
ignition engines and similarly an engine test at standard operating conditions is used. 
Any test fuel is referenced to a blend of n-cetane and 1-methylnaphtalene to find a 
combination that matches in ignition quality [64]. 
DCA additive effectiveness is tested mainly on engine tests. Either 60 hr dyno 
tests or road tests after which the intake valves are weighed for deposit formation. 
Although these tests successfully display the effectiveness of the additive in the intake 
regions, they do not take into account of the CCD either in the same engines or GDI 
equipped engines. According to Barnes et al. [4], difficulties arise from signal to noise 
ratio in such cases but the aforementioned tests in modified forms (such as ASTM D 
6201 standard test) can be carried out. An alternative test that can be carried out is to 
characterise injector fuel flow properties for reference fuel and that of one with an 
additive.
No specified method of testing DRA additives seems to have been developed, 
although an often noted parameter is the frictional pressure drop in pipes or 
alternatively the drag-reduction (DR), which can be expressed as [81]: 
𝐷𝑅 =
∆𝑃
𝑤𝑖𝑡ℎ𝑜𝑢𝑡 𝐷𝑅𝐴
−∆𝑃
𝑤𝑖𝑡ℎ 𝐷𝑅𝐴
∆𝑃
𝑤𝑖𝑡ℎ𝑜𝑢𝑡 𝐷𝑅𝐴
2.2 
Here ∆P stands for a frictional pressure drop in a pipe and DR is expressed as 
a percentage improvement in drag reduction with an additive. 
All fuels need to adhere to a set of standards that would also include a target for the 
electrical conductivity. AS additives can be tested following the procedure outlined 
by the ASTM D4308-12 standard [102]. By this method, a fuel is placed in a cell 
which is connected in series to a power source and a sensitive direct current ammeter 
is used to measure the electrical conductivity.