Effect of Gasoline Fuel Additives on Combustion and Engine Performance

P
re
ss
ure,
 ba
r 
(I
M
E
P
)
P
re
ss
ure,
 ba
r;
 I
nte
ns
it
y
, 
%;
 H
RR,
 
J
/CAD 
Ignition Timing, CAD BTDC
Peak Pressure
Knock Intensity
Peak Heat Release Rate
IMEP

---

4.3 Conclusion 
115 
initially increase and then decrease as the spark was advanced. It is evident that the 
optimal spark timing occurred at 35 CAD BTDC. Although advancing spark further 
resulted in higher measured peak cylinder pressures, Ji et al. [237] describe that the 
negative work on the piston reducing the IMEP values. Similarly, retarding the spark 
results in a retarded peak pressure occurrence and less work can be transferred to the 
piston.
 
The spark timing additionally affected the knock intensity readings. The 
intensity was defined as the percentage of cycles where knocking occurs. As the spark 
was advanced and higher pressures were experienced in the cylinder, more of the 
cycles went through rapid pressure rise that caused the end gases to auto-ignite.
4.3
 
Conclusion 
This chapter aimed to describe in detail the characteristics of base gasoline fuel 
under various fuel injection and combustion strategies and also introduce the 
conditions under which fuel additive study would be undertaken.
Fuel spray atomisation characteristics were investigated through laser 
diffraction technique at ambient pressure and temperature conditions. A fuel quantity 
based method was developed to analyse possible SMD changes caused by additives 
under varying injection pressures between 50 – 110 bar. The results of the additive 
analysis and a selection of pure component fuels are presented in Chapter 5. 
Three combustion strategies were investigated for suitability to analyse effect 
of additives. These included gasoline spray and vapour combustion in the combustion 
vessel and engine testing in a single cylinder research engine. It was found that spray 
combustion in the CVCV could not produce the repeatability levels needed to 
confidently compare additive effects. Therefore, a method based on homogeneous 
mixture of air and gasoline vapour combustion in the vessel under lean conditions was 
developed. Test conditions were determined as 3 ml of fuel per vessel filling with an 
initial charge pressure of 0.7 bar before ignition. Finally, tests under engine conditions 
were carried out. Conditions for the engine testing were summarised in Table 4.1. The 
results of the analysis with additives are presented in Chapter 6.