Fuel additive comprising aliphatic amine, paraffin and cyclic hydrocarbon

A composition suitable for use as a fuel additive is disclosed which comprises at least about 40% by volume of a paraffin which is selected from n-hexane and n-heptane, about 1% to about 20% by volume of aliphatic amine and at least about 5% by volume of cyclic hydrocarbon which has at least five carbon atoms and is liquid at 20.degree. C., said aliphatic amine and cyclohexane having boiling points less than that of said paraffin. The additive improves the combustion process of the fuel such that particulate emission is reduced.

This invention relates to fuel additives. There is a need to reduce the 
type and amount of harmful pollutants formed in the combustion process of 
an internal combustion engine. In an internal combustion engine, on 
complete combustion, hydrocarbon fuels produce carbon dioxide and water 
vapour. However, in most combustion systems the reactions are incomplete, 
resulting in unburned hydrocarbons and carbon monoxide formation. 
Moreover, particulates may be emitted as unburnt carbon in the form of 
soot. Impurities in the fuel are also emitted in the form of oxides, 
typically sulphur oxides. Furthermore, in the high temperature zone of the 
combustion system, atmospheric and fuel bonded nitrogen is oxidised to 
nitrogen oxides, mainly nitrogen oxides and nitrogen dioxide. 
The desired goal of reducing the amount of fall groups of pollutants 
especially HC, Pm and NO.sub.x is very difficult to achieve due to the 
mutually contradictory nature of the formation of these pollutants i.e. to 
prevent NO.sub.x formation requires a depletion of oxygen and to prevent 
HC, Pm requires an abundance of oxygen. 
It will be appreciated that it is very difficult to establish the 
characteristics which are likely to enhance combustion of the fuel because 
of the complex nature of the combustion process. However, to achieve a 
better understanding of the combustion process it is convenient to model 
the process into three distinct zones, namely a preheat zone, the true 
reaction zone and a recombination zone. Degradation of the fuel occurs in 
the preheat zone where the fuel fragments leaving the zone generally 
comprise mainly of lower hydrocarbons, olefins and hydrogen. In the 
initial stages of the reaction zone the radical concentration is very high 
and oxidation proceeds mainly to CO and OH. Also in this region many other 
species are competing for the available atomic oxygen i.e. NO, SO and 
SO.sub.2. The CO and OH species are thermodynamically favoured in reaction 
with oxygen to convert into CO.sub.2 and H.sub.2 O and so these reactions 
will be essentially complete in the early stages of the flame. If 
initiation occurs near the beginning of the reaction zone this will allow 
OH and CO species greater time to react with the available oxygen. 
However, shortening the ignition-delay time will allow all other species to 
give greater time for reaction. This would increase harmful oxide 
emissions--especially so in modern lean burn engines with retarded 
injection. 
Over recent years, great emphasis has been placed on reducing the regulated 
and visible emission. Thus, in general, research has been directed at 
reducing the size of the particulates which are emitted. While size does, 
of course, have an effect on the visibility of these particulates, the 
number of particulates is now realised to have an effect both on 
performance and also health. 
Thus particle number has been linked to a decline in crank case oil 
performance. Vehicles with more advanced emission technologies such as 
higher injection pressures produce higher levels of soot in the lubricant. 
High levels have been identified as the main contributor to viscosity 
increase and wear and this will, in consequence, lead to higher fuel 
consumption and associated emissions. 
The health effects associated with particulate levels have in many 
epidemiological studies shown significant association with a variety of 
human health end points, including mortality, hospital admissions, 
respiratory symptoms, etc. The U.S. six cities study showed a consistent 
and statistically significant relationship to acute mortality and fine 
particles (below 2.5 microns) (PM.sub.2.5) concentrations. Although, much 
research work is needed to understand the underlying biological mechanism 
of the association, it is nevertheless quite apparent that particle number 
concentration and size does have a significant health effect. Reduction of 
total particle number would significantly improve air quality in terms of 
its health effects. 
A number of approaches to improve the emissions have already been adopted 
with varying degrees of cost, applicability and success. However, the most 
desired and widely applicable approach involve the "clean diesel" fuels at 
the current specifications i.e. EM590 that produce regulated emissions 
under standard test cycles. The "city diesel" fuel contains only 0.0003% 
sulphur. 
To achieve this objective, the most convenient and versatile approach is to 
use fuel additives. Already, additive packages of varying performance are 
increasingly used in many European diesel fuels. These additive packages 
give the fuel formulator added degrees of freedom in obtaining the 
designed fuel characteristics and performance. As refining practices 
become more constrained, fuel additives will play an increasing role in 
ensuring that the fully formulated fuel meets and exceeds the legislative 
emission requirements. 
However, most fuel additives used at present are functional i.e. injector 
cleaners, corrosion inhibitors, lubricity modifiers, etc. and do not 
directly influence the combustion process where the emissions are 
essentially produced. Those additives which have claimed performance in 
the combustion system have not conclusively demonstrated their effect or 
are metallic based. It is apparent, though, that metallic additives are 
not the preferred route due to growing evidence of their deleterious 
effect on exhaust oxygen cells and OBD systems. 
According to the present invention there is provided a fuel additive which 
affects the combustion process and thereby reduces the number of particles 
emitted. According to the present invention there is provided a 
composition which comprises at least 40% by volume of a paraffin which is 
n-hexane and/or n-heptane, 1 to 20% by volume of at least one aliphatic 
amine and at least 5% by volume of a cyclic hydrocarbon which has at least 
5 carbon atoms and is liquid at 20.degree. C., said aliphatic amine and 
said cyclic hydrocarbon having boiling points less than that of said 
paraffin. 
The principal component of the additive comprises n-hexane or n-heptane, 
straight chain hydrocarbons. The use of C6-C7 hydrocarbons is very 
specific; thus the use of higher homologues is less advantageous. 
The aliphatic amine used in the present invention is typically a monoamine 
or a diamine, which is typically primary or secondary. It will generally 
have 3 to 8, especially 3 to 6, carbon atoms. The number of nitrogen atoms 
will generally not exceed 2. Preferred amines include secondary monoamines 
and primary diamines, the former being especially preferred. 
Diisobutylamine is particularly suitable. Other suitable monoamines which 
may be employed include isopropyl amine and tertiary butyl amine. These 
amines will typically have a boiling point from 25 to 80.degree. C., more 
preferably from 40 to 60.degree. C. but this depend to some extent on the 
paraffin used which generally has a boiling point no greater than 
200.degree. C. and preferably no greater than 160.degree. C. The amine is 
present in an amount from 1 to 20% by volume. Generally at least 1.5%, 
preferably at least 2.5%, by volume is present. A preferred concentration 
range is 1.5 to 10%, especially 2.5 to 5%, by volume. 
The preferred cyclic hydrocarbons used in the present invention have 6 
carbon atoms. They are preferably saturated. Cyclohexane is especially 
preferred although aromatic hydrocarbons such as benzene and toluene can 
be employed although are generally more expensive. As indicated, the 
cyclic hydrocarbon is present in an amount of at least 5% by volume, 
typically 10 to 30% and especially 15 to 25% by volume. 
The paraffin is present in an amount of at least 40% by volume, typically 
50 to 75% and preferably 55 to 65%. It has been found that it can be 
advantageous to use a mixture of hexane and heptane. In such circumstances 
the hexane generally predominates such that it represents typically 30 to 
40% by volume of the composition while the heptane represents 20 to 30% by 
volume of the composition. 
It will be appreciated that, in general, the composition of the present 
invention is in the form of a liquid solution. 
Higher homologues can also be used provided that they are liquid at 
20.degree. C. 
In addition, the composition can contain other ingredients, typically 
petroleum spirit or kerosene. Desirably, concentration of these additives 
does not exceed 20% by volume. Such additives generally act as a carrier 
for the other ingredients. There is no need for any metal-containing 
compounds in the composition. The presence of alcohols is generally 
undesirable. 
A particularly preferred composition for use in the present invention is as 
follows: 
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n-hexane 35% 
n-heptane 25% 
cyclohexane 20% 
diisobutylamine 3.5% 
petroleum spirit 
16.5%. 
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It has surprisingly been found that the use of the compositions of this 
invention to diesel fuel can reduce the number of particles emitted on 
combustion very significantly. 
The additive composition of the present invention may be included by the 
supplier of the fuel or it may be supplied in a package to be incorporated 
at a later stage, for example at the retail site. In general the additive 
will be employed at a treat rate of from 1:100 to 1:10,000 and preferably 
from 1:500 to 1:5,000, parts by volume of fuel, depending on the nature of 
the fuel. Accordingly, the present invention also provides a fuel which 
comprises the additive composition of the present invention. 
Although the present invention is not bound by any particular theory, it is 
believed that the hexane and heptane will initiate the combustion reaction 
while the cyclic hydrocarbon will control the reaction.

The following examples further illustrate the present invention. 
EXAMPLE 1 
Mercedes Benz MB 220D ECE15+EUDC 
The additive of the invention was evaluated under the ECE 15+EUDC 
conditions in a 1997 model year, 4 cylinder, 2.2 liter engine fitted with 
EGR and Oxidation Catalyst (see Table I for technical data). 
The results obtains were taken after the catalyst and show that the 
additive of the invention consistently reduces regulated emissions. The 
results are shown in FIG. 1. 
Average Reductions Obtained 
Average percentage reductions in emissions with the additive of the 
invention were compared to the average of the base runs i.e. 1 run prior 
to additive treatment and 3 runs on the base fuel after the additive 
treatment. The first base run was compared to historical data and was 
shown to have good repeatability. 
Particles (Pm)=9.5% 
(Hydrocarbon) HC+NO.sub.x =12.1% 
CO=35.7% 
NC.sub.x =6.8% 
HC=28.2% 
TABLE I 
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MERCEDEZ BENZ C220D TECHNICAL DATA 
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ENGINE PERFORMANCE 
Cylinders/Valves per cylinder 
4/4 
Capacity (CC) 2155 
Maximum Power Output (kw/hp @ rpm) 
70 (95)/4800 
Maximum Torque Output (Nm/lbsft @ rpm) 
150 (111)/3100-4500 
Bore/Stroke 89/86.6 
Compression Ratio 22.1:1 
Top Speed (mph/kmh) 109/175 
EQUIPMENT 
ENGINE 
Electronically controlled pre-chamber fuel injection 
Exhaust gas recirculation and oxidation catalyst 
Naturally Aspirated 
Twin overhead camshafts 
Hydraulic valve clearance compensation 
TRANSMISSION 
Five speed manual transmission 
Twin mass flywheel with manual transmission 
WEIGHTS 
Kerb Weight (kg) 1400 
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EXAMPLE 2 
Particle Size and Distribution 
An investigation using the single cylinder Proteus engine (see Table II for 
technical data) was carried out to examine the influence of the additive 
of the invention on reducing the total number of particles. The results 
show that the additive of the invention significantly reduces the total 
number of particles emitted within the Pm2.5 range (see FIGS. 2 and 3). 
TABLE II 
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Proteus Engine Build Specification 
Ricardo Proteus Single Cylinder Research 
Engine Type Engine No. 107 
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Combustion system 
Direct Injection, simulated turbocharger 
and aftercooler 
Rated Power 52 kw at 1900 rev/min 
Peak Torque 310 Nm at 1140 rev/min 
Bore 135 mm 
Stroke 150 mm 
Swept Volume 
2.147 litres 
Cylinder Head 
4 valves per cylinder, Central vertical 
Injection Inlet Swirl Ratio 1.1 Rs 
Valve Timings 
IVO = 15 BTDC, IVC = 35 ATDC, EVO = 50 
BBDC, EVC = 13 ATDC 
Compression Ratio 
16.0:1 
Combustion Chamber 
Open Chamber, 90 mm diameter 
Fuel Injection 
Electronically - controlled common rail 
System system 
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Measurement Techniques 
Aerodynamic Diameter 
The aerodynamic equivalent diameter is defined as the diameter of a unit 
density sphere having the same gravitational settling velocity as the 
particle under analysis. It is measured by time of flight analysers based 
on the assumption that particle inertia is directly linked to its size. 
Thus by accelerating particles under subsonic conditions and recording 
particle transit times the transit aerodynamic size can be determined. 
This measurement is generally used for particles between 0.1 .mu.m and 10 
.mu.m. 
The Scanning Mobility Particle Sizer (SMPS) 
The Scanning Mobility Particle Sizer (SMPS) functions on the basis of the 
movement of gas-borne or aerosol borne particles possessing an electrical 
charge towards an electrode. 
Particles entering the SMPS first pass through an impaction stage to remove 
any particles larger than 1 .mu.m. The aerosol stream then enters a 
neutraliser where the particles are assigned charges. The positively 
charged particles then enter the electrostatic classifier. A given 
particles mobility within an electric field is proportional to its size. 
The SMPS is generally used for measurement of particles between 10 nm and 
450 nm. 
RESULTS 
The data developed in the Proteus engine demonstrates that the additive of 
the invention reduces the total number of particles by over 80% compared 
to base fuel for particles in the range of 10 nm to 450 nm and by over 50% 
for particles in the range 0.45 .mu.m to 4 .mu.m. This is a significant 
reduction. The results for particles in the range of 10 nm to 450 nm are 
shown in FIG. 2. The results for particles in the range of 0.45 .mu.m to 4 
.mu.m are shown in FIG. 3.