Vaporized Fuel Injection System ( VFIS )
For many years, many innovative implementations of vehicle technology such as Direct Injection ( DI ), US Patent 6739309, have been developed to improve efficiency and to minimize pollution. In an endeavor to help meet stringent future emissions standards and growing environmental demands, there is a need to continue to explore a better and more efficient method in improving fuel efficiency and in minimizing pollution.
Why does VFIS system have higher thermal efficiency than Direct Injection System?
Currently, more than 87% energy is dissipated or wasted in the form of heat, drive train loss, and idling loss. Among these energy loss, 62% loss is mainly heat loss. More detailed information of engine efficiency is available in the sites at Fuel Economy.
Because engine inefficiency is mainly due to incomplete combustion and heat dissipation, more focus is required to improve complete combustion and to recover wasted heat energy to perform useful work. To help explain how to improve complete combustion, let's assume that the same amount of gasoline fuel being exposed to the same required amount of air, it is obvious that gasoline fuel being atomized with injector burns much more efficient than gasoline fuel in liquid state due to increased surface area for combustion reaction with oxygen; for the same reason, gasoline fuel being vaporized using heat in combustion chamber such as direct injection will burn more efficient than atomized gasoline fuel for the fact that gasoline fuel is vaporized to its smallest molecular size, namely, maximum surface area achieved, for combustion reaction with oxygen. However, there are still several disadvantages that affect the thermal efficiency of direct-injection gasoline engine as stated below,
At exhaust stroke, tremendous heat energy is inevitably expelled out of combustion chamber to exhaust system while exhaust valve opens.
Inflow of cold air at intake stroke, especially in winter, lowers temperature of combustion chamber, resulting in incomplete vaporization of gasoline for combustion and power loss.
Injection of gasoline fuel into combustion chamber at intake stroke cannot ensure gasoline fuel, especially those with high number of carbon chains, being vaporized completely and mixed with air rapidly for efficient combustion.
So what is the purpose of vaporizing gasoline in vaporization chamber EXTERNALLY? There are many advantages of doing so,
Recovers heat loss partially and puts it back to the combustion system so that temperature inside combustion chamber can be optimally maintained higher than temperature surrounding outside of combustion chamber for efficient combustion.
Inflow of cold air, especially in winter, into combustion chamber causes temperature drop that results in incomplete combustion. VFIS can be programmed, based on temperature of air, to heat gasoline fuel to higher temperature to compensate heat loss so that high-temperature vaporized gasoline fuel, when mixed with cold air in combustion chamber before combustion, will constantly maintain desired temperature of combustion chamber to be the same or above as needed.
Since vaporization process occurs in vaporization chamber, unlike direct injection in combustion chamber, gasoline fuel absorbs/recovers a large amount of heat energy (specific heat and latent heat of vaporization) from radiator/exhaust pipe via heat exchanger. More heat energy will be released after combustion to deliver a powerful stroke to drive the piston downward.
It ensures gasoline fuel being vaporized
completely before gasoline fuel is injected into combustion
chamber, and being mixed with air rapidly before combustion.
To further improve fuel efficiency and to reduce pollution, Vaporized Fuel Injection System, US Patent 6868839, is developed. VFIS SYSTEM INJECTS PRECISE AMOUNT OF 100% VAPORIZED FUEL INTO COMBUSTION CHAMBER AT A PRECISE TIME AND AT AN APPROPRIATELY-SELECTED, AND OPTIMAL HIGH TEMPERATURE/PRESSURE TO AVOID PRE-IGNITING FUEL (i.e. DETONATION) AND PRODUCING NITROGEN OXIDE (NOx), and fuel combustion process will then be complete with no un-burnt hydrocarbon left behind. Therefore, power output will be maximized and air pollution will be minimized. More importantly, VFIS system utilizes wasted heat energy to vaporize fuel, and heat being added to the fuel vaporization chamber will effectively increase the internal energy of fuel so that heat release increases, so does the pressure of the gas mixture, during combustion to drive the piston in the cylinder downward. As a result, fuel efficiency will be substantially increased.
How does VFIS injection system work?
VFIS injection system works very similar to direct gasoline injection that uses combustion chamber as an INTERNAL vaporization chamber to promote about 97% vaporization of gasoline that it claims for combustion; while VFIS injection system employs an EXTERNAL vaporization chamber to promote 100% COMPLETE fuel vaporization for combustion and, more importantly, RE-UTILIZATION of waste energy, a feature that direct gasoline injection can not achieved, boosts more fuel saving than that achieved by direct gasoline injection and Vapor Fuel System that allows engine to run at an incredibly lean 20:1 air fuel ratio.
VFIS implementation is very straightforward using embedded system as ECU to control the operation process, and said ECU can be integrated into vehicle's existing ECU with suitable number of ports provided to control the operation process to further reduce manufacturing cost.
As shown in fig. 1, VFIS system basically includes a fuel vaporization chamber, an upstream fuel injector/valve for injecting fuel to vaporization chamber, a two-way valve and a downstream fuel injector to inject precise amount of fuel to combustion chamber. The vaporization chamber has a first input and a first output, and is connected with a fuel source via the first input. The vaporization chamber vaporizes fuel to desired high temperature and pressure, and then outputs vaporized fuel to the first output. The two-way valve has first and second valve inputs and a valve output. The first valve input is connected to the first output of the fuel vaporization chamber, and the second valve input is connected to the fuel source. The two-way valve is capable of switching to allow fuel in liquid or gaseous state to flow from only one of the first or second valve inputs to the valve output.
To further simplify the implementation of VFIS system, the two-way valve and downstream fuel injector can be replaced with a fuel injector having dual nozzles, US Patent 6273032, by Robert Bosch Gmbh, that is capable of injecting precise amount of gasoline fuel in liquid state with small opening or in gaseous state with larger opening based on signals from ECU. Heat supply may be from various sources such as exhaust pipe, radiator and etc. depending on what types of fuel are used, and how high the temperature of fuel is heated to. Heat flow rate of heat exchanger may also be regulated with a control valve (not shown in fig. 1) depending on signals from ECU which is based on the conditions of temperature and pressure in vaporization chamber.
What types of fuel are appropriate for Vaporized Fuel Injection System?
Renewable fuel such as ethanol*, E85, methanol and fossil fuel such as gasoline and ethanol-blended diesel are working fine to VFIS. Theoretically, the higher temperature the fuel is heated to, the higher percentage the wasted heat energy is recovered**. Therefore, fuels with low boiling point, low flash point, high latent heat of vaporization and high auto-ignition temperature are ideal fuel sources for combustion. Low boiling point ensures that fuel is completely vaporized in vaporization chamber, creating high pressure for injection purpose, low flash point ensures its ability to ignite when mixed with air, high latent heat of vaporization ensures more heat energy can be recovered during vaporization process, and high auto-ignition temperature ensures the highest temperature the fuel could be heated to and is then mixed with air without occurrence of pre-ignition.
Ethanol has low boiling point at 78ºC, low flash point at 14ºC, high latent heat of vaporization at 914KJ/Kg and high auto-ignition temperature at 425ºC. Hence, ethanol is considered to be a perfect fuel source for VFIS. However, heating ethanol to temperature above 200ºC, the functioning of solenoid actuator is critical. As vaporization temperature closes to Curie Temperature, steel is starting to lose its magnetic property. Fortunately, there are new magnetostrictive materials such as Terfernol-D with Curie temperature of 357ºC, and 12% chrome ferritic stainless steel (Ugiperm 12FMTM) with Curie Temperature of ~730ºC available for use in making high-temperature fuel injectors.
With respect to conventional gasoline, it has flash point less than 45ºC, final boiling temperature as high as 225ºC, and auto-ignition temperature at around 245ºC. Since its final boiling temperature and auto-ignition temperature are close, for reason of system stability, it is preferable to vaporize gasoline at temperature ranging between 90ºC (T50) and 150ºC (T90). For this reason, slight modification of VFIS, by adding a fuel separation mechanism as shown in fig. 2 with a fuel-level sending unit 7 testing the depth level of un-vaporized gasoline accumulated in the vaporization chamber, is made to serve the purpose . Between this range of temperature, let's say temperature at T90 is selected, having considered high pressure inside the vaporization chamber, 90% or less of gasoline will be vaporized; and the rest of 10% or more gasoline with higher number of carbon chains, when having accumulated to certain amount in the fuel vaporization chamber, is 'forced out' via a duct connected at the bottom of the vaporization chamber by utilizing gasoline vapor pressure inside, and is fed back directly to fuel injector 1 through a 3-way switching valve 4*** switching at P3 as shown in fig. 2. Upon entering lower-pressure combustion chamber by means of direct injection or port injection, this high-temperature, un-vaporized, highly pressurized gasoline will instantaneously change into gaseous state for complete combustion. Correspondingly, pulse width duration of injector 1 is appropriately adjusted for lean mix purpose as soon as 3-way switching valve 4 switches to P2 and P3 with different parameters to increase fuel economy. Fuel injection pressure of Fuel injector 1 could be maintained at constant by regulating the heat flow rate of heat exchanger and/or by controlling the fuel injection rate of Fuel injector 2 based upon the information provided by both Temperature sensor 5 and Pressure sensor 6. To further stabilize the fuel injection pressure, a pressure regulator , not shown in figures, could be added along the fuel line between Fuel injector 1 and 3-way switching valve 4.
* Ethanol and methanol have very high latent heat of vaporization at 0.913MJ/Kg and 1.154MJ/Kg respectively. Petroleum blended with ethanol/methanol can help recover more heat energy in addition to increasing vapor pressure.
** It is worthy of note if fuel is heated to very high temperature, pressure due to compression in combustion chamber causes auto ignition temperature to drop, and fuel will be pre-ignited. To avoid detonation, it is desirable to keep compression ratio/ temperature within reasonable limits.
*** Fuel Injector 1 and 3-way switching valve 4 can be replaced with the configuration of using a dual-nozzle injector and a 2-way switching valve so that when dual-nozzle injector selects to inject gaseous gasoline fuel, 2-way switching valve will then control the flow of desired gasoline vapor.
Summary of VFIS operation:
a) When vehicle with gasoline direct injection system starts up at cold temperature initially, switching valve 4 switches at position P1 to proceed fuel injection via downstream injector 1 as usual, and VFIS system will not work until temperature inside vaporization chamber rises to minimum pre-determined temperature, tmin , with regulated heating sources from exhaust pipe, engine block, radiator and etc.
b) When temperature rises to minimum temperature, tmin , the upstream injector 2 will start injecting gasoline fuel into vaporization chamber until pre-determined gasoline vapor pressure, p1 , in the vaporization chamber is reached.
c) When pressure rises to pressure, p1 , switching valve switches to position P2 to inject high-temperature gaseous gasoline fuel via downstream injector 1 into combustion chamber for complete combustion, and upstream injector 2 will continue to inject gasoline fuel into vaporization chamber to offset vapor pressure loss simultaneously.
d) When pre-determined maximum gasoline residue (un-vaporized fuel) level, Lmax , is accumulated in vaporization chamber, switching valve 4 switches to position P3 to inject high-temperature un-vaporized gasoline fuel, by means of gasoline vapor pressure in the vaporization chamber, into combustion chamber via a tiny duct that connects switching valve 4 to the bottom of vaporization chamber. Upon entering lower-pressure combustion chamber by means of direct injection or port injection, this high-temperature, un-vaporized, highly pressurized gasoline will instantaneously change into gaseous state for complete combustion.
e) When pre-determined minimum gasoline residue level, Lmin , is reached, switching valve 4 will then switch back to position P2 to continue gaseous fuel injection.
Correspondingly, pulse width duration of downstream injector 1 is appropriately adjusted for lean mix purpose as soon as switching valve 4 switches to position P2 and position P3 with different parameters to increase fuel economy.
Engine technologies and reference:
Fuel Vapor Technology integrated with Hybrid Technology : eVaro - 135mpg
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This site was last updated 07/04/10