Effect of Gasoline Fuel Additives on Combustion and Engine Performance

Figure 3.7: Combustion vessel leakage characteristics at ambient temperature 
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
-0.5
0.5
1.5
2.5
3.5
4.5
P
re
ss
ure,
 ba
r(
g
a
ug
e)
Time, hrs

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3.2 Combustion Experiments 
82 
3.2.1.1
 
Gas Preparation 
Gas conditions in the combustion could be controlled using two methods: 
a)
Heating the air up using an inline air process heater and
b)
Pre-combustion in the vessel under lean conditions.
The heater and the gas mixing manifold can be seen in Figure 3.8. The air process 
heater enabled reaching temperatures of up to 700 °C at the exit from the heater and 
dependent upon set-up inside the combustion vessel and heat losses in the gas injection 
lines, temperatures above 250 °C could be achieved within the chamber for short 
periods of time. Vessel was heated up by running heated high pressure air through the 
Figure 3.8: Top: Farnam air process heater, Bottom: gas mixing manifold 
Gas mixing 
manifold 
Compressed air inlet 
Fuel inlet 
Gas mixing 
manifold secondary 
exhaust 
Pressure 
transducer 
Farnham 
process heater 
Compressed air inlet 
Heater control 
module 
Thermocouple 

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3.2 Combustion Experiments 
83 
system until certain wall and air temperatures were achieved. The low thermal inertia 
of the rig meant that up to 3 hours was required to reach 80 °C wall temperature but 
also that the temperature could be maintained throughout spray and gasoline vapour 
combustion events without experiencing a significant drop. The large volume of the 
vessel (22.5l) enabled large number of spray combustions before oxygen levels were 
depleted to a critical level, thus speeding up experimental time. This was especially 
true for raised initial air pressures. 
The pre-combustion method allowed for much increased pressure and 
temperature conditions for a short time period. A lean mixture of gaseous fuel was 
ignited, giving EGR-like conditions before spray combustion. This method can 
potentially simulate engine conditions better than the heater method but repeat 
experiments under same conditions are time consuming. The pre-combustion gaseous 
fuel mixture could be prepared based on partial pressures. Dalton’s law of partial 
pressures states that the ratio of partial pressures of air and fuel is the same as their 
molar ratio [220]. This can be expressed as: 
𝑃
𝑓
=
𝑛
𝑓
𝑛
𝑎𝑖𝑟
× 𝑃
𝑎𝑖𝑟
3.2 
Generally the pre-combustion method suits better diesel combustion where 
spray variability does not play as much a role as in gasoline combustion where it is 
additionally accompanied by spark variability and as a result a larger number of 
repeats is required for a statistically relevant average [114].
Additionally to spray combustion, a combination of syringe pump and heater 
was used for gasoline vapour combustion. Heated fuel would be pumped at a constant 
rate into the pre-heated vessel where it would evaporate and result in a homogeneous 
air-fuel mixture. Although typical experimental timescales involved were an order of 
magnitude longer per combustion event, the pressure rise from the pre-mixed gasoline 
combustion event was more than 2 magnitudes of order higher. As a result the error 
deriving from limitations in pressure transducer sensitivity was reduced. 
The air-fuel mixing was aided by a 70 mm brass fan, driven by a 1.3 kW 3,000 
rpm electric motor. The fan mount replaced one of the quartz windows to allow for 
improved gas mixing while filling the vessel with pre-combustion gases/ gasoline 
vapour. The fan location is as shown in Figure 3.9. 

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3.2 Combustion Experiments 
84