Patent Application
20170051634
The embodiments described below relate to heat recovery (HR) systems, and more particularly, to a vehicle heat recovery system applied to a non-diesel internal combustion engine, particularly but not exclusively a natural gas internal combustion engine.
The use of natural gas to fuel internal combustion (IC) engines, as opposed to using gasoline or diesel fuels, is becoming more common. The incentives include lower fuel costs and reduced emissions. However there are drawbacks to using natural gas which can include an increase in the space required for carrying fuel and a loss of performance compared to an equivalent diesel vehicle. It is also common that the thermal efficiency of a natural gas engine (especially for homogeneous combustion) is lower than an equivalent diesel engine and that engine out exhaust temperatures are correspondingly higher. It is also common for natural gas engines to require less complex after-treatment equipment than an equivalent diesel engine to meet current emissions standards (for example no SCR) meaning the tail pipe exhaust temperatures are typically much higher than for an equivalent diesel vehicle.
Further, it is increasingly common for natural gas to be stored in a liquid state (Liquified Natural Gas, LNG) on vehicles to maximize the range. The liquid gas is normally evaporated to gas before entering the engine which requires considerable heat input.
It is also known to recover heat energy from a conventional vehicle IC engine using a Rankine cycle. For example, U.S. Pat. No. 4,031,705 discloses a heat recovery system that heats the working fluid using heat from the IC engine's exhaust and the IC engine's cooling circuit, i.e., the IC engine's radiator.
According to a first aspect of the invention, there is provided a system for an engine comprising:
Preferably, the gaseous fuel is natural gas.
Preferably, the fluid is primarily a hydrocarbon, in particular ethanol.
According to a second aspect of the present invention, there is provided an engine system comprising:
Preferably, the gaseous fuel is natural gas.
Preferably, the fluid is primarily a hydrocarbon, in particular ethanol.
According to a third aspect of the invention, there is provided a system for an internal combustion engine comprising:
Such a combination of a natural gas engine vehicle in combination with a heat recovery system where the heat recovery working fluid is also consumed via combustion in combination with the natural gas is advantageous in terms of reduced risk of working fluid degradation over time. Moreover, such co-fuelling may assist the ignition of natural gas in-cylinder and increase vehicle range.
Preferably, the gaseous fuel is natural gas.
Preferably, the fluid is a hydrocarbon, in particular ethanol.
The system may comprise a fuel evaporator for expanding liquefied gaseous fuel into gaseous fuel, the condenser being in thermal contact with the fuel evaporator. This may reduce the requirement for heat rejection in the heat recovery system.
According to a fourth aspect of the present invention, there is provided an engine system comprising:
Preferably, the gaseous fuel is natural gas.
Preferably, the fluid is a hydrocarbon, in particular ethanol.
The system may comprise a fuel evaporator for expanding liquefied gaseous fuel into gaseous fuel, the condenser being in thermal contact with the fuel evaporator.
The figures and following description depict specific examples to teach those skilled in the art how to make and use the best mode of embodiments of a vehicle heat recovery system. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the present description. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the vehicle heat recovery system. As a result, the embodiments described below are not limited to the specific examples described below, but only by the claims and their equivalents.
As shown, the engine 101 is a gas-fuelled internal combustion (IC) engine having pistons that reciprocate in cylinders as indicated at 99 to drive a crankshaft 102. A fan 135 may be coupled to the crankshaft to generate air flow across a radiator 136 for the engine cooling system.
The gas fuel typically natural gas—is stored in compressed liquid form in storage tank 90 from where it is fed (as indicated by arrow F) via a liquid-to-gas evaporator 91 to mix as indicated at 98 with air A supplied by a turbocharger 92, charge cooler 93 and flow valve 94 prior to being fed into the cylinders 99 as is well known.
As is also well known, exhaust from the cylinders is recirculated (EGR) to the engine inlet 103 via EGR flow path 95 and/or fed to the turbocharger 92 and then via treatment system 96 (SCR) and an exhaust flow path/tail pipe 97 to atmosphere E. As shown, treatment system 96 does not employ active regeneration and thus avoids excessive tail pipe temperatures.
First and second evaporators 120, 121 are located within exhaust flow path 97 and EGR flow path 95 respectively. As indicated by arrows W, working fluid is fed to each evaporator from a reservoir or fluid supply 104 via a high-pressure fluid pump 105 in fluid communication with an outlet of the fluid supply 104. The working fluid may include water, refrigerant or ethanol and possibly oil. The number of evaporators utilized is not important for purposes of the present description and should in no way limit the scope of the claims that follow.
The high-pressure fluid pump 105 may be driven by the engine 101 or may be driven by a separate electric motor, for example. The high-pressure fluid pump 105 can elevate the pressure of the fluid from a reservoir pressure to a higher threshold pressure. In some embodiments, the high-pressure fluid pump 105 may raise the pressure of the fluid to a threshold pressure of approximately 30 bar from the reservoir pressure, which is typically at or slightly above atmospheric pressure. However, other threshold pressures are certainly possible and the particular example pressure should in no way limit the scope of the present embodiment.
Heat from the exhaust in the two flow paths 95,97 (which may be at different temperatures) is transferred via evaporators 120,121 to the working fluid, which vaporizes and may become superheated, e.g. at approximately 250° C. and 25 bar. However, those skilled in the art can readily appreciate that these values may vary based on the particular application and should in no way limit the scope of the present embodiment.
The vapor leaves the two evaporators 120,120 and flows (as indicated by arrows X) to an expander 129 where it reduces in enthalpy while expanding, thereby converting at least some of the energy of the vapor to mechanical work/motive power, specifically motion. The expander 129 can comprise one of a variety of well-known devices, such as a turbine, a piston, a vapor engine, such as a rotary vane type vapor engine, etc. The particular type of expander 129 utilized is not important for purposes of the present description and should in no way limit the scope of the claims that follow.
In the embodiment shown, the output shaft of expander 129 is coupled as indicated at 131 to the crankshaft 102 or other suitable component of the engine 101 in order that the motion of the output shaft might drive the crankshaft, adding power to the engine 101.
As shown, the expanded working fluid leaves the expander 129 and travels to a condenser 134 where it is cooled to liquid form prior to being delivered back to the fluid reservoir 104 as indicated by arrow R. Condenser 134 is in thermal contact with the fuel liquid-to-gas evaporator 91 such that the heat released by the cooling working fluid is transferred to the expanding liquid fuel gas. The thermal contact may be direct physical contact, with condenser and evaporator being fixed to or even integral with one another or indirect contact, e.g. through a shared heat transfer medium such as a liquid coolant.
This offers a convenient way of disposing of the working fluid before it reaches the end of its thermodynamically useful life (organic working fluids in particular break down with repeated exposure to the high temperatures in the evaporators). In particular, it can allow the use of shorter life or more heat-sensitive working fluids. Reservoir 104 can be replenished with working fluid at the same time as the storage tank 90 is replenished with liquified gas. A hydrocarbon, in particular ethanol, may be a suitable working fluid. In the case of a motor vehicle, using the working fluid as an additional fuel source will also increase the range of the vehicle between refueling stops.
Moreover, the working fluid can also provide combustion assistance to the gas: in particular, when diesel engines are converted to run on natural gas, they are often equipped with spark ignition systems or co-fuelled with a compression ignition fuel in order to run. The working fluid can assist fuel ignition. This may be particularly relevant also for cold starting. A hydrocarbon, in particular ethanol, may be suitable for this purpose.
Not only does this offer a convenient way of disposing of the working fluid before it reaches the end of its thermodynamically-useful life, potentially allowing short-life or more thermally-sensitive working fluids to be used, it also reduces the number of different fluids, reduces the need for cooling and reduces complexity.
Although specific embodiments are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the present description, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other heat recovery systems, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the embodiments described above should be determined from the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1406803.5 | Apr 2014 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2015/051115 | 4/13/2015 | WO | 00 |
