LPG Data

THEORETICAL COMPATIBLE PROPANE/AIR MIXTURES

The table below shows Propane/Air mixtures, compatible with natural gas with several different specific gravities and calorific values.
All figures are approximate and are given for Propane with specific gravity of 1.53 and calorific value of 2516 BTU/cuft.

Natural Gas		Propane / Air Mixture
SGU	BTU/cuft	% LPG	% Air	SGU	BTU/cuft
0.56	800	47.54	52.46	1.252	1196
	850	50.87	49.13	1.270	1280
	900	54.24	45.76	1.287	1365
	950	57.65	42.35	1.306	1450
	1000	61.11	38.89	1.324	1538
	1050	64.62	35.38	1.342	1626
	1100	68.16	31.84	1.361	1715
	1150	71.76	28.24	1.380	1805
	1200	75.40	24.60	1.400	1897
0.58	800	46.62	53.38	1.247	1173
	850	49.88	50.12	1.264	1254
	900	53.18	46.82	1.282	1338
	950	56.52	43.48	1.300	1422
	1000	59.90	40.10	1.317	1507
	1050	63.33	36.67	1.336	1593
	1100	66.80	33.20	1.354	1681
	1150	70.32	29.68	1.373	1769
	1200	73.88	26.12	1.392	1859
0.60	800	45.76	54.24	1.243	1151
	850	48.95	51.05	1.259	1232
	900	52.18	47.82	1.276	1313
	950	55.45	44.55	1.294	1395
	1000	58.76	41.24	1.311	1478
	1050	62.12	37.88	1.329	1563
	1100	65.51	34.49	1.347	1648
	1150	68.95	31.05	1.365	1735
	1200	72.43	27.57	1.384	1822

Natural Gas		Propane / Air Mixture
SGU	BTU/cuft	% LPG	% Air	SGU	BTU/cuft
0.62	800	44.93	55.07	1.238	1130
	850	48.06	51.94	1.255	1209
	900	51.23	48.77	1.272	1289
	950	54.43	45.57	1.288	1369
	1000	57.68	42.32	1.306	1451
	1050	60.97	39.03	1.323	1534
	1100	64.29	35.71	1.341	1618
	1150	67.66	32.34	1.359	1702
	1200	71.07	28.93	1.377	1788
0.64	800	44.15	55.85	1.234	1111
	850	47.22	52.78	1.250	1188
	900	50.32	49.68	1.267	1266
	950	53.47	46.53	1.283	1345
	1000	56.65	43.35	1.300	1425
	1050	59.87	40.13	1.317	1506
	1100	63.13	36.87	1.335	1588
	1150	66.44	33.56	1.352	1672
	1200	69.78	30.22	1.370	1756
0.66	800	43.41	56.59	1.230	1092
	850	46.42	53.58	1.246	1168
	900	49.47	50.53	1.262	1245
	950	52.55	47.45	1.262	1322
	1000	55.68	44.32	1.295	1401
	1050	58.84	41.16	1.312	1480
	1100	62.04	37.96	1.329	1561
	1150	65.27	34.73	1.346	1642
	1200	68.55	31.45	1.363	1725

Properties of		Natural Gas	Propane	Butane
Chemical formula		CH₄	C₃H₈	C₄H₁₀
Boiling point of liquid at atmospheric pressure	°F °C	-259 -162	-44 -42	32 0
Specific Gravity of vapor (Air = 1)		0.6	1.53	2.00
Specific Gravity of liquid (Water = 1)		0.6	0.51	0.58
Calorific value @ 60 °F (15°C)	BTU/cuft kcal/m³MJ/m³	1012 9005 37.71	2516 22,390 93.74	3280 29,189 122.21
	BTU/gal kcal/liter MJ/liter		91,690 6,103 25.56	102,032 6,792 28.44
	BTU/lb kcal/kg MJ/kg		21,591 11,995 50.22	21,221 11,789 49.36
Latent heat of vaporization	BTU/gal kcal/kg MJ/kg kW/kg		785 102.9 0.431 0.1196	808 105.9 0.444 0.1231
Liquid weight	lbs/gal kg/liter		4.24 0.508	4.81 0.576
Vapor volume from 1 gallon of liquid at 60 °F Vapor volume from 1 liter of liquid at 15 °C	cuft m³		36.39 0.272	31.26 0.234
Vapor volume from 1 lb. of liquid at 60 °F Vapor volume from 1 kg of liquid at 15 °C	cuft m³		8.547 0.534	6.506 0.406
Combustible limits	% of gas in air	5 - 15	2.4 - 9.6	1.9 - 8.6
Amount of air required to burn 1 cuft. of gas Amount of air required to burn 1 m³ of gas	cuft m³	9.53	23.86	31.02
Ignition temperature in air	°F °C	1200 650	920 - 1020 490 - 550	900 - 1000 480 - 540
Maximum flame temperature in air	°F °C	3568 1964	3595 1980	3615 1991
Octane Number		100	Over 100	92
All data is approximate. For actual properties of any particular batch, contact your fuel supplier.

Approximate Vapor Pressure in psig
Temperature		Propane ----> To ----> Butane
° F	° C	100%	95/ 5*	80/ 20	70/ 30	60/ 40	50/ 50	40/ 60	30/ 70	20/ 80	100%
-40	-40.0	1.5	1.4	1.2	1.1	0.9	0.8	0.6	0.5	0.3
-30	-34.4	5.6	5.3	4.5	3.9	3.4	2.2\8	2.2	1.7	1.1
-20	-28.9	10.7	10.2	8.6	7.5	6.4	5.4	4.3	3.2	2.1
-10	-23.3	16.7	15.9	13.4	11.7	10.0	8.4	6.7	5.0	3.3
0	-17.8	23.5	22.3	18.8	16.5	14.1	11.8	9.4	7.1	4.7
10	-12.2	31.3	29.7	25.0	21.9	18.8	15.7	12.5	9.4	6.3
20	-6.7	40.8	38.8	32.6	28.6	24.5	20.4	16.3	12.2	8.2
30	-1.1	51.6	49.0	41.3	36.1	31.0	25.8	20.6	15.5	10.3
40	4.4	63.3	60.3	51.2	45.2	39.2	33.2	27.1	21.1	15.1	3.0
50	10.0	77.1	73.6	63.1	56.0	49.0	42.0	35.0	28.0	20.9	6.9
60	15.6	92.4	88.4	76.2	68.2	60.1	52.0	43.9	35.8	27.8	11.6
70	21.1	109	105	90.8	81.6	72.3	63.1	53.9	44.6	35.4	16.9
80	26.7	128	123	107	96.5	86.0	75.5	65.0	45.5	43.9	22.9
90	32.2	149	143	125	113	101	89.4	77.5	65.6	53.6	29.8
100	37.8	172	165	145	132	118	105	91.3	77.9	64.4	37.5
110	43.3	197	189	167	152	137	122	106	91.4	76.3	46.1
* HD5, Commercial Grade Propane

Temperature Conversion Table

°F

°C

°F

- 50

- 45.6

- 50

- 58

- 40

- 40.0

- 40

- 30

- 34.1

- 30

- 22

- 20

- 28.9

- 20

- 4

- 10

- 23.3

- 10

- 17.8

+ 10

- 12.2

+ 10

- 6.7

- 1.1

+ 4.4

104

10.0

122

15.6

140

21.1

158

26.7

176

32.2

194

100

37.8

100

212

110

43.3

110

230

120

48.9

120

248

130

54.4

130

266

140

60.0

140

284

150

65.6

150

302

160

71.1

160

320

170

76.7

170

338

180

82.2

180

356

190

87.8

190

374

200

93.3

200

392

212

100

210

410

Formula:

Degrees C = (°F - 32) x 5/9
Degrees F = 9/5 x °C + 32

BTU content of common fuels
	Per Pound	Per Gallon
Propane	21,591	91,690
Butane	21,221	102,032
Gasoline	20,930	110,250
Fuel Oil #1	16,960	135,425
Diesel	18,500	142,800

Butane Equivalents
Unit	BTU	Pound	Therm	Dekatherm	Cuft.	Gallon
1 Pound =	21,221	1	0.212	0.0212	6.50	0.208
1 Therm =	100,000	4.714	1	0.1	30.64	0.98
1 Dekatherm =	1,000,000	47.14	10	1	306.4	9.8
1 Cuft. =	3,280	0.1537	0.032	0.0032	1	0.03199
1 Gallon =	102,032	4.81	1.02	0.1020	31.26	1

General Information
1 Lb. Steam	970 BTU
1 Boiler HP (per hr)	33,475 BTU
1 Kilowatt Hour	3,412 BTU
1 Gallon, Water	8.337 lbs
1 Cubic Foot, Water	7.481 gallons
1 Cubic Foot	1,728 cubic inches
1 Gallon	231 cubic inches

Propane Equivalents
Unit	BTU	Pound	Therm	Dekatherm	Cuft.	Gallon
1 Pound =	21,591	1	0.216	0.0216	8.58	0.239
1 Therm =	100,000	4.622	1	0.1	39.7	1.10
1 Dekatherm =	1,000,000	46.22	10	1	397	11.0
1 Cuft. =	2,516	0.1164	0.025	0.0025	1	0.027
1 Gallon =	91,690	4.24	0.917	0.0917	36.39	1

Specific Gravity and Heat Content by Volume of LP Gas-Air Mixtures

Propane - Air Mixtures
% Propane	% Air	Specific Gravity	Gross BTU/cuft
100	0	1.530	2516
95	5	1.504	2390
90	10	1.477	2264
85	15	1.451	2139
80	20	1.424	2013
75	25	1.398	1887
70	30	1.371	1761
65	35	1.345	1635
60	40	1.318	1510
59	41	1.313	1484
58	42	1.307	1459
57	43	1.302	1434
56	44	1.297	1409
55	45	1.292	1384
54	46	1.286	1359
53	47	1.281	1333
52	48	1.276	1308
51	49	1.270	1283
50	50	1.265	1258
49	51	1.260	1233
48	52	1.254	1208
47	53	1.249	1183
46	54	1.244	1157
45	55	1.239	1132
40	60	1.212	1006
35	65	1.186	881
30	70	1.159	755
25	75	1.133	629
20	80	1.106	503
15	85	1.080	377
10	90	1.053	252
5	95	1.027	126
0	100	1.000	0

Butane - Air Mixtures
% Butane	% Air	Specific Gravity	Gross BTU/cuft
100	0	2.000	3280
95	5	1.950	3116
90	10	1.900	2952
85	15	1.850	2788
80	20	1.800	2624
75	25	1.750	2460
70	30	1.700	2296
65	35	1.650	2132
60	40	1.600	1968
59	41	1.590	1935
58	42	1.580	1902
57	43	1.570	1870
56	44	1.560	1837
55	45	1.550	1804
54	46	1.540	1770
53	47	1.530	1738
52	48	1.520	1706
51	49	1.510	1672
50	50	1.500	1640
49	51	1.490	1607
48	52	1.480	1574
47	53	1.470	1542
46	54	1.460	1509
45	55	1.450	1476
40	60	1.400	1312
35	65	1.350	1148
30	70	1.300	984
25	75	1.250	820
20	80	1.200	656
15	85	1.150	492
10	90	1.100	328
5	95	1.050	164
0	100	1.000	0

Propane (30%) Butane (70%)
% LPG	% Air	Specific Gravity	Gross BTU/cuft
100	0	1.859	3051
95	5	1.816	2898
90	10	1.773	2746
85	15	1.730	2593
80	20	1.687	2441
75	25	1.644	2288
70	30	1.601	2136
65	35	1.559	1983
60	40	1.515	1831
59	41	1.507	1800
58	42	1.498	1769
57	43	1.490	1739
56	44	1.481	1709
55	45	1.473	1678
54	46	1.464	1647
53	47	1.455	1617
52	48	1.447	1587
51	49	1.438	1555
50	50	1.430	1525
49	51	1.421	1495
48	52	1.412	1464
47	53	1.404	1434
46	54	1.395	1404
45	55	1.387	1373
40	60	1.344	1220
35	65	1.301	1068
30	70	1.258	915
25	75	1.215	763
20	80	1.172	610
15	85	1.129	458
10	90	1.086	305
5	95	1.043	153
0	100	1.000	0

All data is based on the
following assumptions:

Propane Vapor

SGU = 1.53
2516 BTU/cuft

Butane
Vapor

SGU = 2.00
3280 BTU/cuft

Engineering Units Conversion Factors

Multiply		By	To Obtain
Pressure
Atmospheres	atm	1.0332	Kilogram per cm²
	atm	14.70	Pounds per square inch
	atm	404.189	Inches of Water
Inches of Mercury	inHg	0.4912	Pounds per square inch
Inches of Mercury	inHg	1.134	Feet of Water
Inches of Water	inWC	0.0361	Pounds per square inch
	inWC	0.0735	Inches of Mercury
	inWC	0.5776	Ounces per square inch
Kilo Pascals	kPa	0.01	bar
kg per cm²	kg/cm²	14.22	Pounds per square inch
Pounds per square inch	psi	0.06805	Atmospheres
	psi	0.07031	Kilogram per cm²
	psi	6.8948	kPa
	psi	0.06895	bar
	psi	2.036	Inches of Mercury
	psi	27.68	Inches of Water
Length
Centimeters	cm	0.3937	Inches
Feet	ft	0.3048	Meters
Feet	ft	30.48	Centimeters
Feet	ft	304.8	Millimeters
Inches	in	2.54	Centimeters
Inches	in	25.4	Millimeters
Kilometers	km	0.6214	Miles
Meters	m	1.094	Yards
Meters	m	3.281	Feet
Meters	m	39.37	Inches
Miles, nautical	mls	1853.0	Meters
Miles, statute	mls	1609.0	Meters
Miles, statute	mls	5280	Feet
Miles, statute	mls	63360	Inches

Multiply		By	To Obtain
Length (continued)
Yards	yrd	0.9144	Meters
Yards	yrd	91.44	Centimeters
Volume
Cubic centimeter	cm³	0.061023	Cubic inches
Cubic feet	cuft	7.48	Gallons (US)
Cubic feet	cuft	28.316	Liters
Cubic feet	cuft	1728	Cubic inches
Cubic feet	cuft	0.037037	Cubic yards
Cubic feet	cuft	0.028316	Cubic meters
Gallons (UK)	gal	1.20095	Gallons (US)
Gallons (US)	gal	0.13368	Cubic feet
Gallons (US)	gal	0.83267	Gallons (Imperial)
Gallons (US)	gal	3.785	Liters
Gallons (US)	gal	231	Cubic inches
Liters	l	0.03531	Cubic feet
Liters	l	0.2642	Gallons (US)
Liters	l	1.057	Quarts (US)
Liters	l	2.113	Pints (US)
Pints (US)	pnt	0.4732	Liters
Miscellaneous
BTU	BTU	252.0	Calories
Calories	kcal	3.968	BTU
Kilogram	kg	2.205	Pounds
Kilowatt Hour	kWh	3412	BTU
Ounces	oz	28.35	Grams
Pounds	lb	0.4536	Kilograms
Pounds	lb	453.5924	Grams (metric)
Pounds	lb	21600	Propane BTU

Definitions

Several characteristics affect Liquified Petroleum Gas (LPG) as a replacement fuel. These include:

Flame Velocity and Color
Specific Gravity
Calorific Value
BTU Measurement (Wobbe Index)

1. Flame Velocity and Color

Because of the different number of carbon atoms in propane, propane-air mixtures produce a flame that is more yellow in color than that of natural gas. However, the yellow tips are not of any consequence and do not affect burner operation or efficiency. Flame velocities of LPG are near equal to that of natural gas. Therefore, there is no significant flame lift difference between natural gas and propane-air mixtures.

2. Specific Gravity

The density of gas, relative to air, is called specific gravity. The specific gravity of air is defined as 1. Since propane gas has a specific gravity of 1.5, propane-air mixtures have a specific gravity of greater than 1. The chart on the right indicates heat value in BTU per cubic foot, kcal per cubic meter, and the specific gravities of various propane-air mixtures.

Propane - Air Mixtures
BTU/cuft Kcal/Nm³	% Propane by Volume	% Air by Volume	% Oxygen by Volume	Specific Gravity of Mixture	Wobbe Index US Units SI Units
1700 15,130	66.67	33.33	6.694	1.349	1464 13,027
1650 14,685	64.70	35.30	7.378	1.338	1426 12,695
1600 14,220	62.74	37.26	7.787	1.328	1388 12,340
1550 13,795	60.78	39.22	8.197	1.318	1350 12,016
1500 13,350	58.82	41.18	8.606	1.308	1312 11,673
1450 12,950	56.86	43.14	9.016	1.297	1275 11,384
1400 12,450	54.90	45.10	9.246	1.287	1234 10,974
1350 12,015	52.94	47.06	9.835	1.277	1195 10,632
1300 11,580	50.98	49.02	10.245	1.267	1155 10,288
1250 11,135	49.02	50.98	10.654	1.257	994 9,932

LP - Air Mixtures (LP with 30% Propane / 70% Butane)
BTU/cuft Kcal/Nm³	% LP Vapor by Volume	% Air by Volume	% Oxygen by Volume	Specific Gravity of Mixture	Wobbe Index US Units SI Units
1800 16018	59.00	41.00	8.588	1.507	1466 13049
1750 15574	57.36	42.64	8.931	1.493	1432 12747
1700 15129	55.72	44.28	9.275	1.479	1398 12441
1650 14684	54.08	45.92	9.618	1.465	1363 12133
1600 14239	52.45	47.55	9.962	1.451	1328 11822
1550 13794	50.81	49.19	10.305	1.436	1293 11509
1500 13349	49.17	50.83	10.648	1.422	1258 11193
1450 12904	47.53	52.47	10.992	1.408	1222 10874
1400 12459	45.88	54.12	11.335	1.394	1186 10552
1350 12014	44.25	55.75	11.678	1.380	1149 10226

Different heat values result primarily from differences in specific gravity. The higher the specific gravity, the heavier the gas. Since burner orifices, flow meters, regulators, etc. have fixed openings, they allow less flow of heavier gas and therefore must have a higher heat value to provide the same energy input as a lighter gas.

Most natural gas has an average heat value of approximately 1050 BTU/cuft (9350 kcal/m³) and a specific gravity of 0.6 (nominal). Compatible propane-air replacement should have a heat value of approximately 1450 BTU/cuft (12,467 kcal/m³) and a specific gravity of 1.297.

3. CALORIFIC VALUE

The calorific value is the measurement of the amount of heat or energy produced, and is measured either as gross calorific value or net calorific value. The difference being the latent heat of condensation of the water vapor produced during the combustion process. Gross calorific value assumes all water produced during the combustion process is fully condensed. Net calorific value assumes the water leaves with the combustion products without being fully condensed.

Since most gas burning appliances cannot utilize the heat content of the water vapor, gross calorific value is of little interest. Fuel should be compared based on the net calorific value. This is especially true for natural gas, since increased hydrogen content results in high water formation during combustion.

4. WOBBE INDEX

The Wobbe Index, a critical factor when analyzing Propane-Air plant requirements, is a function of gas quality and allows matching one gas (in this case, natural gas) to a replacement gas (in this case, Propane-Air). If the two different gases have an identical Wobbe Index, they will produce an equal amount of heat and combustion products and will require the same amount of combustion air. Burners, adjusted for a specific calorific value and fitted with a replacement orifice to match a lower Wobbe Index, result in minor combustion changes. Substituting a gas for one with a higher Wobbe Index, generally allows a narrow acceptance range. Flame characteristics determine the acceptance range for the replacement gas.

The Wobbe index is defined as:

and is used to compare the energy input into an appliance with different composition fuel gases. If two fuels have identical Wobbe indices, then for a given burner pressure, the energy input will also be identical.