Effect of Gasoline Fuel Additives on Combustion and Engine Performance

2.4.2.3
 
Constant Volume Combustion Vessel (CVCV) 
Non-piston based systems include mainly Constant Volume Combustion 
Chambers (CVCVs) either set for pre-combustion or heated conditions. The chamber 

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2.4 Combustion Analysis 
64 
sizes vary although typically a much larger working section volume than in an engine 
is utilised. Constant volume heated chambers (CVHC) tend to be smaller in size due 
to low thermal inertia of the usually stainless steel walls and high energy needs in 
heating the vessel [114]. Conditions suitable for diesel combustion can be reached, 
with temperatures and pressures of over 590 
°
C and 75 bar, respectively, having been 
reported in the literature [174, 175]. In constant volume pre-combustion chambers 
(CVPC), a pre-determined mixture of lean stoichiometry fuels is combusted to reach 
high temperatures and pressures and the fuel is injected into the products of the 
preceding combustion and ignited [176]. Heated chambers can run repeat experiments 
at much higher frequency than pre-combustion chambers while pre-combustion 
chambers can achieve experimental conditions faster and simulate engine-like 
conditions closer. It has been reported that that compared to other optical methods, 
CVCV allow for highest degree of control over the test conditions and the subsequent 
reduction in variables makes the technique very well suited for fundamental 
combustion studies [113, 114]. 
2.4.3
 
Optical Diagnostic Techniques 
The following sections offer a brief overview of techniques used in optical 
combustion investigations. The methods most relevant to current project are direct 
imaging of flames, shadowgraphy and Schlieren imaging. Shadowgraphy and 
Schlieren imaging both utilise backlight illumination as the light source making use 
of the change in the density gradient in the working section resulting from either sprays 
or combustion. A brief description of a few other methods is additionally given in 
Section 2.4.3.4.