I think it would work on the 3.6 vvt but i would ask the kit maker first
http://www.cira.wvu.edu/afvtp/AFV_proprev.html Detailed descrption of LPG as a motor fuel. Root dirs contain other alt fuel info.
WVU's AFVTP - Propane Review
West Virginia University's
Alternative Fuel Vehicle Training Program
Return to AFVTP Home Page.
INTRODUCTION
GENERAL INFORMATION
LPG (Liqufied Petroleum Gas) is a petroleum derived, colorless gass, typically comprised of primarily either propane, butane, or a combination of the two. LPG has been and continues to be the most widely used alternative motor fuel to gasoline and diesel on a worldwide basis. The acceptance it has enjoyed over the years ensures the place of LPG in clean air scenarios worldwide. Currently, (1992) there are over 500,000 vehicles using propane gas in the United States, most are spark-ignition engines adopted to use either propane or gasoline, and over three million worldwide.
The term propane will be used to refer to LPG.
LPG IN U.S.A
Propane fuel for vehicles is actually a mixture of various hydrocarbons which are gasses at atmospheric pressure and temperature but which liquify at higher pressures. It is one of several mixtures referred to as liquifed petroleum gases (LPG) and is named for the major constituent, propane.
Virtually all U.S, LPG fuel vehicles use propane, thus LPG generally refers to propane gas whose chemical composition is C3H8. LPG is a natural derivative of both natural gas and crude oil. In the United States, approximately 30 % of the LPG is generated during oil refining and 70 % is from natural gas processing and reserves. Domestic production accounts for over 85 % of the LPG supply [10].
In the United States there are more than 10,000 retail propane refueling stations, while in Canada there are about 5,000 stations. Ferrelgass, the second largest propane retailer in the US, operates a fleet of 2,400 vehicles. Of those 2,300 are dedicated propane vehicles, consisting of medium-duty trucks and light-duty pickups. Schimidt reports that Runzheimer International conducted a survey of 118 fleet managers with an avarage of 449 vehicles in each fleet, propane was by far the most frequently named alternative fuel as shown by the results given in Table 1.
Table 1. Alternative fuels selected by fleet managers ( Percent )
Propane CNG Electric Methanol
Business 86 14 29 0
Utility 71 36 36 14
Government 77 22 33 11
In the United States, the propane industry has attemped to adopt an automotive propane standard known as HD5. [1] Fuel for spark ignition engines must meet certain requirements as set out in the HD5 specification. The standard is not universally observed. Because, the concentration of propane as high as virtually 100 %, to as low as 50 % in certain locations. Much of the remainder of the gas is butane and some other hydrocarbons, both saturated and unsaturated. The utilization of LPG as an automotive fuel varied very widely from one country to another, depending on the cost and availability of the fuel in relation to alternative fuels, notably gasoline and diesel, Table 2.
Table 2. LPG Composition ( % by volume ) as Automotive Fuel in Europe
Country Propane Butane
Austria 50 50
Belgium 50 50
Denmark 50 50
France 35 65
Greece 20 80
Ireland 100 _
Italy 25 75
Netherlands 50 50
Spain 30 70
Sweden 95 5
United Kingdom 100 _
Germany 90 10
Source: Urban 1982
HD5 requires minimum propane content of 90 % and propylene content of less than 5 % (volume basis). The remainder is normally n-butane,with isobutane and butanes also present. The limitation on propylene and other propane unsaturates results its low octane number that means low knock resistance, see Table 3. A second cocern with propylene is its photochemical reactivity, which is higher than that of propane. This could be an important factor in formation of smog. Propylene does not occur in LPG obtained from natural gas processing plants but it is found in the LPG resulting from petroleum refinery operations. The minimum propane requirement arises from the need to have sufficient vapor pressure, even at very low temperatures, to deliver fuel to the engine. Vapor pressure of butane is considerably less than that of propane at any given temperature and will not provide adequate pressure for proper equipment operation below about 18-19 C (a minimum of about 0.2 Mpa absolute pressure is required for satisfactory operation of delivery system ).
Table 3. Octane numbers of LPG Components.
Component Research Motor Est. max. ratio comp
propane 111.5 100 11:1
n-butane 95 92 8:1
isobutane 100.4 99 9:1
propylene 100.2 85 7.5:1
n-butane-1 100 80 6.5:1
n-butane-2 101 83 7:1
regular gasoline 92.95 83-86 9:1.
COMPARISION OF PROPANE TO GASOLINE
Performance and drivebility of propane vehicles is essentially the same as for gasoline vehicles. For propane, the gas displacement effect is 4%, it means that the displacement of air by propane causes reduction in power of 4 % (volumetric efficiency decrease) from an equilevent gasoline counterpart. Gasoline on the other hand, provides evaporotive cooling of the intake air which increases the intake air density and increases the power. Test results show 6 % less power with propane than with gasoline[11]. Propane has a research octane rating of 110 to 120, thus, it resists engine knock better than gasoline (gasoline 87-94 ) allowing a higher compression ratio for the engine, see Figure 1. Propane contains about 5 % more energy per unit mass however the density is nearly 32 % less. The net result is that a litre propane contains 28 % less energy than a litre of gasoline, Table 4. Assuming that an engine is operated on propane and gasoline with equal efficiency, more litres of propane will be consumed to provide equilevent performance. Fortunately, engines generally operate on propane with greater efficiency than on gasoline so that the increase in fuel volume is not as great as the energy comparison suggests. Propane fueled vehicles can achieve the same driving range as a gasoline vehicle by installing a slightly larger tank. Propane use consumes approximately 5 % more fuel for equivelent performance but it costs 15 % less than gasoline. Projections for the next decade, anticipate LPG prices increasing far more more slowly than gasoline[11].
Table 4. Energy Density Comparision
HD5-propane Gasoline
Liquid Density * 499 732
kg / m3
Lower Heating Value 46.3 43.9
Mj / kg
Energy Density 23.1 32.2
Density at 20 C & corresponding sat. pressure
The flammability range for propane is from 2.4 to 9.6 % in air. This compares to a flammability range for gasoline of 1 to 7.6 % in air. The ignition temperature, a identification of anti-knock-property, of propane ( 457 C ) is at the higher end of ignition temperature range for gasoline ( 227 to 471 C ).
Gasoline, being a normal liquid, exhibits very little change over the normal temperature or pressure range. Propane, however, is gas at normal temperatures and pressures. Its physicsal properties depend strongly on the temperature and pressure at which they are being stored. The vapor pressure and liquid density of propane are shown in Fig 2 and Fig 3. The first figure defines the pressure that will exist in a propane fuel tank as the ambient temperature changes. The second figure shows why propane tanks can not be filled completely. Some ullage space must be left in the tank because the liquid volume expands significantly if the tank encounters increasing ambient temperatures. Between 27 and 99 F, for example, the liquid volume expands by 13 %. Due to this, and its lower density, propane requires a 35 % greater storage volume than gasoline. Propane systems have some kind of safety fill stop device to limit tank fills to no more than 80 % to 85 % of tank volume. This allows room for liquid expansion if the temperature rises after the tank is filled. Due to the low viscosity of propane and its storage under pressure, it may leak through small cracks, pumps, seals and gaskets more readily than gasoline.
Propane fuel systems, being totally enclosed and pressure tight, have no of refueling, evaporative, running losses and emissions from the fuel storage system.
It is not sufficient to merely consider mass of exhaust emissions. One must also consider how hydrocarbon emissions and nitrogen oxides combine in the atmosphere to form smog.Smog is a ground level photo chemical ozone phenomenon that is a consequence of emissions and sunshine in a relatively stagnant air basin. The less the rate of reactive organic gas emitted, the les ozone formed in time. No ozone is formed without oxides of nitrogen being present and there is a certain ratio of reactive organic gas to NOx that maximizes the ozone formed per unit mass of each of the reactive organic gases. This ratio is often near this optimum in many urban enviroments. Reactive organic gas emission controls are important in reducing the mass and virulance of the compounds. NOx controls are important in minimizing the rate at which ozone is formed from any reactive organic gas and instrumental in minimizing the spread and duration ozone episode. Since, smog is not directly emitted, most emission standards and test procedures fail to make a rational connection with the health oriented air quality standard for ozone. Smog forming potential is estimated by calculating the atmospheric reactivities of each of the individual components in a vehicle`s exhaust emission. Such calculations show a clear-cut advantage for propane, Fig 4. Every gallon of gasoline that can be replaced by propane should cut typical exhaust ozone potential by almost one-half. The high ratio of hydogen to carbon, in popane results in lower production of both toxic carbon monoxide and carbon dioxide, which is the principal greenhouse gas. As a result HC, CO and CO2 emission are lower with propane but NOx emission is higher than with gasoline, Fig 5.
COMPARISION OF PROPANE AND NATURAL GAS
Natural gas vehicle fuel is stored on the vehicle in either the form of compressed natural gas (CNG) stored in cylinders at 2400 to 3600 psi or liquefied natural gas (LNG) stored in tanks at 10 to 30 psi and -163 C
Pipeline quality natural gas is composed of several different gases, of which methane typically accounts for 85 to 95 % . Other hydrocarbons present in natural gas include ethane, propane, some butanes, and trace amounts of other hydrocarbons. Nitrogen, helium, carbon dioxide and trace amounts of hydrogen sulfide, water and odorants are also present. The removal of all CO2, water, hydrogen sulfide and odorants is required for liquefaction, thus LNG does not contain these constituents.
The specific gravity of natural gas relative to air (air = 1.00) is 0.56 to 0.62 depending on gas composition. This indicates that natural gas is lighter than air. In the event of a natural gas leak, the gas will rise and dissipate given open conditions. Propane vapors are heavier than air (specific gravity = 1.5) thus propane will stay low, against the ground and may collect in sewers and other low areas before ultimately dispersing into the air with the aid of wind or ventilation systems.
Natural gas has a research octane rating of about 130 (research octane rating of propane is between 110-120) making it more resistant to engine knock. The anti-knock property is a result of the high ignition temperature, resistance to autoignition, and the relatively low flame speed of natural gas. Methane can be used at higher compression ratios (therefore higher efficiency) than gasoline, propane falls between the two.
The volumetric air- fuel ratio for CNG is 9.6. One cubic meter of fuel is required for every 9.6 cubic meters of air charged. Because the fuel gas must displace air, CNG results in volumetric reduction of about 9.3 % with a corresponding drop in potential power (for propane 4 %).
With respect to almost all defined fuel characteristics, values for propane lie between those for methane and gasoline, Table 5.
The volumetric heating value of the fuels, the volumetric air/fuel ratios, and the volumetric heating values of the stoichometric air/fuel mixtures for different gaseous fuels are shown in Table 6 and Fig 6.
Table 5. Comperative Engine Use Charecteristics
Units Methane Propane Gasoline
Autoiignition point F 1,000-1,350 874 365
Autoignition point C 538-732 468-494 185
Flammability Limits vol percent 5-15 2.1-9.5 1.4-7.6
Stoichometric A/F kg / kg 17.3 15.3 14.7
Stoichometric A/F m3/m3 9.7 24.6
Research octane number 130 112-125 91-95
Motor octane number 105 97-111 82-88
Relative CO2/Btu 0.76 0.92 1.0
Table 6 illustrates the fact that the power obtainable from an engine is more a function of the amount of air that can be charged than of the heating value of the particular fuel being used.
Table 6 Volumetric Heating Value (LVH) of fuel gases and energy content of
stoichometric mixtures with air
Fuel gas Calorific Value Air required m3/ m3 Energy content Mj/m3
Propane 93.2 24.65 3.63
Octane 233.3 59.50 3.92
Natural Gas 31.7 8.53 3.32
Methane 35.9 9.67 3.36
If compared according to emissions data, both methane and propane engines may emit more NOx. NOX is primarily a function of peak combustion temperature. Gasoline enters the combustion chamber at least partially as liquid. The energy used to vaporize the gasoline results in a lower peak combustion temperature. Methane is also considered to contribute to greenhouse gases because methane is a highly persistent and highly absorbtion gas that collects in the upper atmosphere.Propane is oxidized more quickly and generally does not reach upper atmosphere levels. The non-toxic methane has near zero reactivity in the production of photochemical smog, but propane represents a more reactive exhaust hydrocarbon component than with methane.
COMPARISION OF PROPANE AND METHANE TO GASOLINE
The first line in the Table 7 gives the ratio of the energy of the fluids under typical fuel tank conditions, to that of gasoline. In computng this number, the liquid density of saturated propane at 60 F was used. For methane calculations a tank pressure of 3,660 psi was assumed. From line 2 in Table 7, methane requires 3.85 times as much storage volume as gasoline, propane requires 35 % greater storage volume than gasoline.
Table 7.Comparision of Energy Storage Efficiency
Units Methane Propane Gasoline
Energy density ratio to gasoline 0.26 0.74 1.0
Tank volume for 20 GGE Gal 76.9 27.0 20
Tank weight for 20 GGE Lb 530 89 25
Ullage and heel limits percent 4 15 0
Corrected tank volume for 20 GGE Gal 80 31.8 20
Effective energy density raio 0.25 0.63 1.0
Effective tank volume ratio 4.0 1.59 1.0
Weight of fuel lb 107 115 124
Corrected tank weight, 20 GGE lb 552 * 99 25
Full tank weight lb 659 214 149
* 4 tanks, each 20 gallons, Al / Fiberglass
GGE = Gallons of gasoline equilvalent
Natural gas and propane are generally considered to reduce engine maintenance and wear in spark-ignited engines. The most commonly cited benefits are extended oil change intervals, increased spark plug life, nd extended engine life. Natural gas and propane both exhibit reduced soot formation over gasoline. Reduced soot concentration in the engine oil is believed to reduce abrasiveness and chemical degradation of the oil.Gasoline fueled engines ( particularly carburated engines ) require very rich operation during cold starting and warm up. Some of the excess fuel collects on the cylinder walls, " washing " lubricating oil off wals and contributing to accelerated wear during engine warm up [11]. Gaseous fuels do not interfere with cylinder lubrication.
Gaseous fueled engines are generally considered easier to start than gasoline engines in cold weather. Because they are vaporized before injection to into engine. However, under extremely cold temperatures, there is cold-start difficulty for both propane and narural gas.This is probably due to ignition failure because very difficult ionazation conditions, sluggishness of mechanical components. Hot starting can present difficulties for gaseous fueled vehicles, especially in warm weathers. After an engine is shut down, the engine coolant continues to absorb heat from the engine, raising its temperature. If the vehicle is restarted within a critical period after shutdown, ( long enough for the coolant temperature to rise, but before the entire system cools ), the elevated coolant temperature will heat the gas more than normal, lowering its volumetric heating value and density. This would result in mixture enleanment.
PROPANE FUEL SYSTEM EQUIPMENT
A) MIXER
Early propane mixers operated as a conventional venturi-controlled devices in a manner quite similar to gasoline carburetors. Vaporizerd propane is drawn through a fixed orifice in response to engine air flow. The basic design priciples have remained unchanged over 30 years. As intake air enters the engine, a venturi effect is created through the mixer air-valve. This slight pressure drop acts on a spring-loaded diaphragm is lifted proportionally with air flow,. This may be best described as a highly accurate flow meter which controls engine fuel flow as a function of air flow.
B)VAPORIZER
Vaporizer converts the liquid propane to a gas. The primary heat source for this vaporazation is engine-jacket water which flows through specially designed water jackets cast into the vaporizer body. It is necessary that propane fuel systems draw from the bottom of the tank rather than the top. If engine feed were drawn from the gas phase, the heavier, higher boiling components in LPG would gradually become concentrated in the liquid phase creating a liquid mass with a for vapour pressure and a high freezing point .This liquid would create various problems in the feel feed system .Therefore, L.P.G systems draw from the bottom of the tank and send the liquid through a vaporizer that is heated by engine coolant.
C) REGULATOR
The function of the regulator is to provide precise fuel pressure regulation to the mixer in two stages.As demand on the regulator increases with engine load, regulator allows higher flow; demand on system decreases, regulator restricts flow to maintain flow pressure.
D) FUEL TANK
Propane fuel tank is installed, along with a refueling port, fuel lines, and pressure safety valves. A filter" fuelock" removes particles that may be present in the propane.Propane tanks are constructed of heavy gauge steel, in compliance wih the Boiler and Pressure Vessel Code of the American Soceity of Mechanical Engineers ( ASME ) to whitstand a pressure of 1000 psi. Normal working pressures of the tanks vary depending upon ambient temperaturesand the quantity of fuel in the tank, propane systems normally limit the liquid level to 80% of tank total tank volume by astopp fill valve. Common operating pressures are in the range of 130-170 psi. Tanks are equipped with pressure relief valves that will relase propane vapors to the atmosphere to prevent tank explosion under abnormaly high pressure conditions.
SAFETY
In evaluating safety aspects of a fuel with particular reference to its suitibility as automotive fuels, the following overall charectiristics need to be considered.
1) STORAGE AND PORTABILITY CHARACTERISTICS:
Propane as liquid as stored in the tanks on board automobiles. If engulfed in a a fire its heating will result in a rapid increase in pressure, even if the outside twmperature is not too excessive in accordance with its vapor pressure charestiristics. This may require venting the excessive build-up of pressure through appropriate relief valves. On the other hand CNG being a gas requires no relief valves normally and its heating will go merely towards increasing the pressure in accordance with gas laws.
Moreover, LPG operation has potential safety problems at very low temperature starting in comparision to CNG. This is mainly because there is likelihood for excessive build-up of unburnt liquid fuel that will not disperse readily; hence it can lead to uncontrollable fire on ignition.
2) THE TENDENCY TO FORM A COMBUSTIBLE MIXTURE FOLLOWING ACCIDENTAL DISCHARGE:
The release one unit volume of propane in air would generate a maximumm mixture that is around 2.5 times more than the volume of the mixture formed following the release of a similar amount methane vapor.
The extent of hazards associated with such an leakage will depend largely on the relative tendency of the fuel to form a combustible mixture and the length of time for this mixture to persist in the vicinity of discharge and away from it either to be ignited from numerous potential ignition sources or feed a fire that may be engulfing the tank.
The tendency for the fuel to disperse in the surroundings from a leak is governed by the role of buoyancy and diffusional effects.
Due to the propane vapor is heavier than air, it causes to disperse for too slowly, if compared to CNG. The diffusion velocity of any fuel vapor or gas along a specificed concentration gradient in the atmosphere is proportional to the characteristics diffusion coefficient of the gas. Methane is superior to propane, see Table 8.
Propane, when involved in a leak situation will discharge in a liquid form requiring a period of time to vaporize and disperse. In the case of CNG leak, because of the gaseous nature of the fuel , the gas will issue as a very high velocity jet into surroundings aiding greatly in the rapid dispersion of the fuel.
Table 8. Some Properties of Propane, Methane, Gasoline
Property Propane Methane Gasoline
Specific Gravity at NTV 1.52 0.55 4.0
Relative to Air
Normal Boiling Point (K) 231 111.46 ~ 310-478
Critical Pressure (atm) 41.9 45.4 24.5-27
Density of Liquid at NTP (kg / L) 0.5077 0.4225 ~ 0.70
Density of Gas at NTP (kg / m3 ) 1.96 0.6512 ~ 4.40
Density Ratio, NTP Liquid / NTP Gas 259 649 ~ 150
Diffusion Coefficients in NTP 0.10 0.16 ~ 0.05
air ( cm 2 / s )
Diffusion Velocity in NTP Air ( cm / s ) ~ 0.34 ~ 0.51 ~ 0.17
3) IGNITION EXPLOSION AND FLAME SPREAD CHARACTERISTICS:
It takes a minimum of from over 2 % by volume of propane in air at ambient conditions to just support a continuous flame propagation, as compared to around 5 % for methane and 1 % for gasoline. The ignition energy for propane , as well as methane and gasoline, being considered are sufficiently low that ignition is usually assured in the presence of thermal ignition sources such as sparks, lighted matches, hot surfaces and open flames.The quenching of methane-air flames by cold surfaces, as indicated by quenching distance ,see Table 9, is easier than in the case of flames involving propane-air mixtures. Due to this, flame traps are more succesfull in suppressing methane fires than those involving propane.
Table 9. Some Combustion Properties of Propane, Methane, Gasoline
Property Propane Methane Gasoline
Quenching Gap in TNP Air, mm 1.78 2.03 2.0
Limits of Flammability in Vol, % 2.1-10.4 5.3-15 1-7.6
Limits of Detonation in Air Vol, % 3.4-35 6.3-13.5 1.1-3.3
Minimum Energy for Ignition in Air 0.305 0.29 0.24
(mj)
Autoignition Temperature, (K) 740 813 501-744
Flame Temperature in Air, (K) 2243 2148 2470
Maximum Burning Velocity in NTP 43-52 37-45 37-43
Air, cm / s
Energy of Stoichometric Mixture, 3.79 3.58 3.91
Mj / m3
The maximum therotical energy available from a chemical explosion involving methane-air is below half of that propane-air mixtures.
4) SOME ENVIROMENTAL CONSIDERATIONS:
Propane fires tend to persist within the leakage area due to its liquid and heavier than air air states. Methane has relatively low combustion temperatures and its fire hazards do not persist for long due to buoyant and dispersive nature of the fuel.
For fuel line ruptures, pressurized gaseous fuels represent higher hazard levels than gasoline.
In collisions, CNG is the safest fuel, LPG the next, and gasoline the worst.
SUMMARY
In this rewiew, propane, as an alternative fuel is compared to methane and gasoline.
REFERENCES
1) J.E Sinor Cosultants, Inc Niwot, CO, Technical Evaluation and Assesment of CNG / LPG Bi-Fuel and Flex-Fuel Vehicle Vialability.
2) G.A.Karim, Some Considerations of the Safety of Methane, (CNG), as an Automotive Fuel-Comparision with Gasoline, Propane and Hydrogen operation, S.A.E Paper.No 830267
3) G.A.Karim and I. Wierzba, Comperative Studies of Methane and Propane as Fuels for Spark Ignition and Compression Ignition Engines, S.A.E Paper No. 831195
4) James.S. Wallace, Assesment of" First Generation Propane Conservation Equipment, S.A.E Paper 892144
5) Fred Hendren, Propane power for Light Duty Vehicles: An Overview, S.A.E Paper No. 830383
6) Bernie W. Rice, Evaluation of Automotive Stop Fill Valves for Propane Vehicles, S.A.E Paper No. 861576
7) Algas Carburetion, Handbook
8) NPGA # 1331, Commercial / Industrial Propane Guide
9) Science Applications International Corparation, Introduction to Alternative Fuel Vehicles
10) Wilson. B, Evaluation of Aftermarkets Fuel Delivery Systems for Natural Gas and LPG Vehicles
11) J.E Sinor Consultants Inc, The Clean Fuels Report, November 1992, Volume 4, No. 5
[This message has been edited by engine man (edited 09-22-2009).]
