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Cetane Index Calculator

Diesel fuel quality assessment - ASTM D976 / D4737 / EN 15195

40-55

EN 590 range

D976/D4737

Methods

⛽ Fuel type and reference presets

/// measured fuel properties

Density at 15°C (ASTM D1298)

kg/m3

T10 - 10% distillation point (ASTM D86)

°C

T50 - 50% distillation point (ASTM D86)

°C

T90 - 90% distillation point (ASTM D86)

°C

Flash point (ASTM D93)

°C

Sulfur content (ASTM D5453)

mg/kg

Viscosity at 40°C (ASTM D445)

mm2/s

Aromatics content (ASTM D5186)

% vol

Cetane Index (ASTM D4737)

Enter fuel properties to calculate

CETANE SCALE (30 - 75)

30 - Very poor 40 - Min spec 51 - EN 590 55 - Premium 70 - GTL/synthetics

/// cetane number estimator from molecular composition

Cetane Number (CN) vs Cetane Index (CI): CN is measured by ASTM D613 engine test (expensive, ~$2,000/test). CI is calculated from distillation and density data per ASTM D976 or D4737 and correlates well with CN for conventional petroleum diesel (±2 CN units typically). CI cannot be used for oxygenated fuels (biodiesel, alcohols) or additized fuels.

/// molecular class composition (% vol)

n-Paraffins (n-alkanes)

% vol

iso-Paraffins (branched)

% vol

Naphthenes (cycloalkanes)

% vol

Mono-aromatics

% vol

Di-aromatics (naphthalenes)

% vol

Poly-aromatics (3+ rings)

% vol

/// diesel blend cetane index calculator (up to 4 components)

Blending rule: Cetane Index blends approximately linearly by volume fraction. Cetane Improver additives (2-EHN, di-tert-butyl peroxide) can raise CN by 3-8 units at 0.1-0.5% dose. Biodiesel (FAME) has higher CI (~55-65) but lower energy density.

Cetane improver additive (2-EHN equivalent)

% vol

/// diesel fuel quality comparison - global specifications

Parameter	EN 590 (EU)	ASTM D975 No.2	IS 1460 (India)	Unit	Test method
Cetane Number (min)	51	40	51	-	ASTM D613
Cetane Index (min)	46	40	46	-	ASTM D4737
Density at 15°C	820-845	820-850	820-845	kg/m3	ASTM D1298
T95 distillation (max)	360	338	360	°C	ASTM D86
Flash point (min)	55	52	35	°C	ASTM D93
Sulfur (max)	10	500	10	mg/kg	ASTM D5453
Viscosity at 40°C	2.0-4.5	1.9-4.1	2.0-5.0	mm2/s	ASTM D445
CFPP (max, winter)	-20	-	-	°C	EN 116
PAH (max)	8	-	11	% wt	IP 391
Lubricity (max, HFRR)	460	-	460	µm	EN ISO 12156
FAME content (max)	7	5	7	% vol	EN 14078
Net calorific value (min)	~42,600	~42,500	~43,000	kJ/kg	ASTM D240

/// cetane number of pure compounds

Compound	Class	CN	Boiling point (°C)	Notes
n-hexadecane (cetane)	n-paraffin	100	287	CN reference standard = 100
n-dodecane (C12)	n-paraffin	74	216	High CN, jet fuel range
n-tetradecane (C14)	n-paraffin	95	254	Very high CN
Isocetane (2,2,4,4,6,8,8-heptamethylnonane)	iso-paraffin	15	240	CN reference = 15
Decalin (decahydronaphthalene)	naphthene	48	189	Moderate CN
1-methylnaphthalene	di-aromatic	0	241	CN = 0, strong inhibitor
α-methylnaphthalene	di-aromatic	-2	244	Negative CN - antiknock
Toluene	mono-aromatic	5	111	Strong CN depressant
n-butyl benzene	mono-aromatic	17	183	Low CN aromatic
FAME (methyl palmitate)	ester	74	415	Biodiesel component
FAME (methyl oleate)	ester	59	349	Unsaturated FAME
2-EHN (cetane improver)	nitrate ester	~200	227	Additive: +3-8 CN at 0.1-0.5%

/// ASTM D4737 four-variable cetane index formula

ASTM D4737 (recommended, 4-variable):
CI = 45.2 + 0.0892 x (T10N) + [0.131 + 0.901 x B] x (T50N) + [0.0523 - 0.420 x B] x (T90N) + 0.00049 x [(T10N)^2 - (T90N)^2] + 107 x B + 60 x B^2

where:
T10N = T10 - 215 | T50N = T50 - 260 | T90N = T90 - 310
B = exp(-0.0035 x (rho15 - 850)) - 1
T10, T50, T90 = 10%, 50%, 90% distillation temperatures (°C) per ASTM D86
rho15 = density at 15°C (kg/m3) per ASTM D1298 / D4052

ASTM D976 (2-variable, older, less accurate):
CI = 454.74 - 1641.416 x D + 774.74 x D^2 - 0.554 x B + 97.803 x (log B)^2
where D = density at 15°C (g/mL) | B = T50 (°C)

Applicability: ASTM D4737 is valid for:
- Petroleum-derived middle distillates (diesel, kerosene, jet fuel)
- Density range: 800-900 kg/m3
- T10: 150-280°C | T50: 200-320°C | T90: 280-380°C
- NOT valid for: biodiesel (FAME), oxygenated fuels, additized fuels
- Accuracy: ±2 CN units vs measured CN (ASTM D613) for conventional diesel

/// cetane number and engine combustion - engineering guide

CN Range	Classification	Ignition delay	Applications	Combustion issues
< 35	Very poor	> 5 ms	Industrial boilers only	Severe knock, white smoke, high HC
35-40	Poor	3-5 ms	Non-road, older engines	Cold start problems, knock, noise
40-46	Acceptable	2-3 ms	Minimum for EN 590	Marginal cold start, moderate noise
46-51	Good	1.5-2 ms	Standard EN 590 diesel	Normal operation
51-55	Very good	1-1.5 ms	Premium diesel, EURO 6 vehicles	Excellent cold start, low noise
55-65	Excellent	< 1 ms	High-performance engines, GTL	Near-ideal combustion
> 65	Premium / Synthetic	< 0.8 ms	GTL, synthetic paraffinic fuel	May need pre-injection management

/// effect of cetane number on engine performance

Engine parameter	CN increases from 40 to 55	Mechanism
Cold start ability	Major improvement	Shorter ignition delay reduces crank time needed
Combustion noise (diesel knock)	-5 to -8 dB(A)	Less premixed charge at ignition = softer pressure rise
HC and CO emissions	-10 to -20%	More complete combustion during ignition delay
NOx emissions	-2 to -5%	Lower peak pressure and temperature
Fuel consumption	-1 to -2%	Improved combustion phasing
Particulate (PM) emissions	-5 to -10%	Better air-fuel mixing during delay period
White smoke (cold start)	Eliminated	Complete oxidation of unburned fuel droplets

petrosmartacademy.com · ASTM D4737 / D976 / D613 / EN 590 · Educational tool - verify results with certified laboratory