Surface heat flux measurements for short time-period on combustion chamber with different types of coaxial thermocouples

ABSTRACT

The K, E, and J-types of coaxial thermocouples have been designed and fabricate to perform transient heat flux evaluation at the combustion chamber of a four-stroke diesel engine. These coaxial thermocouples are quite efficient in short-duration transient measurements due to the response time of these instruments are in the rage of milliseconds or less. Using water plunging technique, the thermal product and time constant of these handmade coaxial thermocouples have been evaluated as well as compared with available literatures. The transient temperature signals are recorded form K, E, and J-type coaxial thermocouples on the combustion chamber of a four-stroke internal combustion engine for short duration of 200 ms. The transient heat fluxes are acquired from transient temperature signals with the help of one-dimensional heat conduction formulation for a semi-infinite solid body. The errors in the estimated heat flux and transient temperature have been observed as 3% and 0.5 %, respectively, which are relatively small and acceptable. This signifies that the heat flux values are depending upon the temperature measured by coaxial thermocouple junction as well as also depending on time rate. This survey asserts the heat flux measurement capability of coaxial thermocouple during the combustion process on the internal combustion chamber of a four-stroke diesel engine.

KEYWORDS:

• Coaxial thermocouple
• thermal product
• time constant
• heat flux measurements
• internal combustion engine

Nomenclature

c	=	= specific heat (J/kgK)
k	=	= Thermal conductivity (W/mK)
$q_s$	=	= surface heat flux (W/m2)
t	=	= time(s)
T	=	= Temperature (K)
S	=	= Sensitivity (µV/°K)
$T_s\left(t\right)$	=	= Temperature function of time
ρ	=	= density (kg/m3)
β	=	= effective thermal product (J/m2s0.5K)
τ	=	= dummy time variable (s)
${\tau }_c$	=	= Time constant (milliseconds)
${\alpha }_0$	=	= thermal coefficient of resistance (/°K)