Cochin laboratory

CALORIFIC VALUE (GCV &NCV)

By Bomb (P 6, D 240, IP 12)

By calculation (P 7, D 4868)

Provides information on heat producing capacity of the fuel. The heat of combustion is a direct measure of fuel energy content and is determined as the quantity of heat liberated by the combustion of a unit quantity of fuel with oxygen in a standard bomb calorimeter. A high calorific value is obviously desirable in oil used for heating purposes. The calorific value of residual fuel oil is lower than that of lower-boiling fuel oil because of the lower atomic hydrogen-to-carbon ratio and the incidence of greater amounts of less combustible material, such as water and sediment, and generally higher levels of sulfur. The empirical calculation is based on the correlation between heat of combustion and density, sulfur, water, and ash content of the fuel sample.

GCV: It is the quantity of heat liberated when a unit mass of fuel is burned in oxygen at constant volume, the products of combustion being Carbon dioxide, Nitrogen, Sulphur- dioxide and water.

NCV: It is the quantity of heat liberated when unit mass of fuel is burned in oxygen, the products of combustion being carbon-dioxide and Nitrogen. This value may be expressed either at constant pressure or constant volume.

CALCULATION
Qv = 12400 – 2100 d^2, ( Qv ⁼ Gross Calorific Value, cal/gm & d = Density at 15 deg. C)
Q p = qv – H(WL –C)

H = Hydrogen content , H = 26 -15 d, d = Specific gravity of the sample

W = No of grams of water formed per gram of Hydrogen (Equal to 9), L = latent Heat of vaporization of water (=Equal to 585), C = Correction factor for change in volume from initial to final products. (Equal to 220)
HEAT OF COMBUSTION OF FUEL CORRECTED FOR SULPHUR, WATER AND ASH CONTENT
Qv (Gross) = qv-0.01qv(W+A+S) + X(S)

Qp (Net) = qp-0.1qp(W+A+S) =X(S) - Y(W)

(X = 22.5 when Q is expressed in cal/gm, Y = 5.85 when Q is expressed in cal/gm)
CARBON RESIDUE (CCR, RCR & MICRO METHOD)

The carbon residue value of burner fuel serves as a rough approximation of the tendency of the fuel to form deposits in vaporizing pot- and sleeve-type burners. Similarly, provided alkyl nitrates are absent, the carbon residue of the diesel fuel correlates approximately with combustion chamber deposits. The carbon residue value of motor oils, while once considered useful, is now considered to be of doubtful value because of the presence of additives in many oils. The carbon residue of gas oil is useful as a guide in the manufacture of gas from gas oil and residue value of crude oil residuums, cylinder and bright stocks, are useful in the manufacture of lubricants.