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Pao Chi Pien
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kelly The E-V diagram of my original comment has not been reproduced by the Green Car Congress. The limited-pressure diesel cycle p-v diagram, 1-2-3a-3b-4-1 can be changed to 1-2-3a’-3b’4-1 E-V diagram with the constant-pressure combustion portion 3a-3b replaced by the constant-E combustion process 3a’-3b’. Then the combustion temperature T (E3a/cv) will not over the critical temperature of NOx formation. I assume that the existing IFCE of IC engine is 25% and the expected IFCE of the CI-CVCE RICE range from 68.5 to 61.7% depends on the power/torque output as shown in line 8 of table 1. The purpose of my comment is to give my feedback to DOE in defining the scope of the final solicitation. I hope to see more comments from the readers of Green Car Congress on the energy transformation equation E2/E1 = (V1/V2)k-1.
Without a correct theory of reciprocating internal combustion engine (RICE), none of DOE funded vehicle technologies programs can achieve intended goals. When the working fluid of a RICE undergoes a compression, combustion, or expansion process, the conservation of energy law assures that the products of p1/p2, V1/V2, and T2/T1 remain unchanged even cylinder gas has no time to reach equilibrium. Since p2/p1 = (V1/V2)k and cvT2/cvT1 is equal to E2/E1, E2/E1 = (V1/V2)k-1 and V2/V1 = (E1/E2)1/(k-1) where E is the total internal energy contained within total cylinder volume V. Both E and V are state variables. At state 1 of an adiabatic cycle 1-2-3-4-1, E1 is equal to the average cylinder temperature times the specific heat under constant volume cv. Using E2/E1 = (V1/V2)k-1, E2 is calculated. During a combustion process 2-3, heat energy Q converted from fuel chemical energy, increases E3 to E2 + Q and increases V2 to V3 with V3 = V2(E2/E3)1/(k-1). At state (4), E4 = E3(V3/V4)k-1. Based on internal energy E balance, IFCE = (E3 – E4)/E3 or 1 – E4/E3. The fact that IFCE of a RICE, having any engine configuration and using any fuel, can help DOE to reach the goals of the vehicle technologies programs.
Engineer-Poet The E-V plot computed by E2 = E1(V2/V1)k-1 and using internal energy balance for computing fuel energy conversion efficiency could double fuel efficiency. Then there is no immediate need for electric vehicles.If you are interested, I will be more than glad to sent you more information.
The reciprocating internal combustion engine (RICE) has been, and continues to be, analyzed and evaluated utilizing thermodynamic principles and tools. Rather than a thermodynamic system, however, the RICE can be more accurately viewed as a mechanical system with mechanical work being transformed into the cylinder gas internal energy, and vise versa. When so viewed, analysis and evaluation of the RICE is greatly simplified. Moreover, when the RICE is evaluated as a mechanical system, it is possible to design RICE that achieves significant increases in efficiency over existing engines. Traditionally, the equivalent air cycle of RICE is modeled with a pressure-volume diagram. From the perspective of power production, however, the equivalent air cycle should be modeled by a plot of total internal energy E versus total volume V. More specifically, during an adiabatic compression process 1-2, a moving piston compresses cylinder gas from V1 to V2 doing compression work to change E1 to E2. with E2 = E1 (V1/V2)k-1 with E1 equal to the average ambient T1 times the constant volume specific heat cv. This equation E2 = E1 (V1/V2)k-1 is directly derived from the mechanical work done when cylinder volume changes from V1 to V2 without involving absolute temperature T. Therefore it can be applied to real gas. For a constant volume combustion process 2-3, at point 3, V3 = V2, E3 = E2 + Q. For a constant-pressure combustion, at point 3, E3 = E2 + Q/k and V3 = V2(E3/E2). For a limited-pressure combustion process 2-3a-3b, E3a = E2 + x and E3b = E3a + y with x + yk = Q and E3b/E3a = V3/V2. E3a and E3b are obtained by solving these two equations. An expansion process begins at point 3b, with E4 = E3b(V3/V4)k-1. The indicated fuel conversion efficiency is equal to (E2 + Q – E4)/(E2 + Q). It should be noted that E4 is determined by expansion ratio and E2 is determined by compression ratio. Compression ratio and expansion ratio are independent of each other. For more complete fuel combustion, a high compression ratio is chosen to obtain a compression temperature just below the fresh point of the fuel/air mixture. An appropriate fuel equivalence ratio is chosen to limit the combustion temperature for avoid NOx formation and excessive heat loss to coolant. A high expansion ratio is chosen for reducing E4 For each energy transformation process, cylinder volume determines the cylinder gas total internal energy and a plot of E-V can be produced. This fact has greatly simplified the reciprocating internal combustion engine in theory and practice. After the combination of compression ratio, fuel equivalence ratio, and expansion ratio has been chosen, the only thing a engine designer has to do is to shorten the combustion time as much as practical for achieve the maximum possible fuel efficiency with minimum emissions. It is hoped that those readers thinking about all electric vehicles would comment on the E-V plot and the internal energy balance for computing indicated fuel conversion efficiency.
For doubling of CAFE, it is necessary to design automotive engines based on sound theory rather than based on engine experiments alone.For a reversible adiabatic process in an ideal gas from state (1) to state (2), T2/T1 = (V1/V2)k-1 where T2 and T1 are in equilibrium. Then internal energy E is equal to cv(T2 – T1. There is no time for working fluid of a reciprocating internal combustion engine to reach equilibrium state, the equation T2/T1 = (V1/V2)k-1 can not be applied to reciprocating engines. Instead of adding heat to a gas to increase internal energy E, internal energy E can also be increased by work done on the gas. A moving piston can compress a gas within a long cylinder from V0 to V, the compression work W done is equal to the definite integral of pdV from V0 to V with p equal to the average pressure within the volume. Regardless of the actual p distribution, the average pressure p is equal to p0(V0/V)k (Boyle’s law). Then, W = p0(V0)k(1/V)k-1/(k-1) (1) E = p0(V0)k/(k-1)(1/V)k-1/J (2) E2/E1 = (V1/V2)k-1 (3) With W = 0 at Vo, Equation (1) is the mechanical work done on the gas. Equation (2) shows total internal energy E as a function of the total volume V. Lastly, Equation (3) is obtained by taking the ratio of two internal energies at two different volumes. Equation (3) can be applied to non-equilibrium thermodynamics. As such, the new equation can be applied as a powerful new tool in evaluating existing engines, as well as, in designing new high efficiency engines. To analyze the performance of a reciprocating internal combustion engine, an E-V diagram is computed by using Equation (3). At the beginning of a compression process 1-2, E1 = cvT1 is already known where T1 is the average absolute temperature. At point 2, E2 = E1(V1/V2)k-1 where k is the weighted average value of k values of component gases of working fluid. During a combustion process 2-3, fuel chemical energy is transformed into heat energy to increase the internal energy, with E3 = E2 + Q where Q is equal to the fuel burned per cycle times the heating value of burned fuel. At the end of the expansion process 3-4, E4 = E3(V3/V4)k-1. Based on internal energy balance, the indicated fuel conversion efficiency is (E3 – E4)/E3. By clearly showing the internal energy value at the beginning and end of the each of the compression, combustion, and expansion processes, the E-V diagram (constructed using the equation E2/E1 = (V1/V2)k-1) provides a simple and direct roadmap for how to increase indicated fuel conversion efficiency.
Besides seeking unconventional fossil energy resource, it is also important to achieve the maximum possible fuel efficiency with minimum emissions for existing engines. Basically, a reciprocating internal combustion engine is a device to convert fuel chemical energy into useful mechanical work. Currently, less than 25% of fuel chemical energy is transformed into mechanical work. Because working fluid properties are not in equilibrium and non-equilibrium thermodynamics is too complicated for practical use, model-based design tools and development processes based around them have been used to generate some success for automotive companies. However, without scientific guidelines, such tools have reached point of diminish return. Furthermore, technologies such as downsizing, variable compression ratio and lean-burn engine operation, etc. obtained from engine experiments can not be easily incorporated into one practical engine design. I have developed a new key equation to relate the work done by or on a moving piston and the increase or decrease of working fluid internal energy. By using this key equation to obtain three key variables and create a new engine configuration to allow these three key variables to vary, the maximum possible fuel efficiency with minimum emissions can be achieved. I first obtain the optimum combination of three key variables to achieve accurate prediction of the highest possible indicated fuel efficiency. Then by minimizing the coolant load experimentally, the brake power is maximized. By doing so, the fuel efficiency can be doubled without retooling factories.
Fuel chemical energy is converted into heat energy to increase the internal energy of cylinder gas by a combustion process. Only a small portion (about 25%) is transferred into brake power. A major portion of converted heat energy is transferred into coolant load. For a GDI engine operating at one-third load, the thermal efficiency is same as at full load. Because of much lower combustion pressure and temperature, the coolant load per unit power output is much smaller. Operating at one-third load, a GDI engine can save 50% fuel as compared with that at full load. An automotive engine should be designed at one-third load to have enough power to propel a middle size car at 70 mph speed on highway and to provide full power momentarily when needed. A technical document full describing this matter can be obtained by request.
Many of the listed 26 supported areas for research activities have been pursued experimentally for decades with billions of dollars already spent. It is not likely that further significant fuel saving and emission reduction can be obtained by engine experiments alone without applying thermodynamics principle. Because the thermodynamic properties of working fluids of real engine are not in equilibrium, the equilibrium thermodynamics seems having no use at all. However, for thermodynamic analysis of a reciprocating engine performance, it is only required to know the average value of the temperature rather than the temperature distribution as described below. The reciprocating internal combustion engine is a device to convert fuel chemical energy into mechanical work. Even though combustion taking place inside the cylinder, it is equivalent to combustion taking place out side the cylinder and the converted heat being transferred to the gas inside the cylinder. The heat so transferred is denoted by Q+. The ensuing expansion process converts a part of the thermal energy into mechanical work. The remaining part of the thermal energy is rejected from the cylinder at the end of expansion process. The heat transferred from inside the cylinder to the outside by the exhaust gas is denoted by Q-. By definition, the thermal efficiency is equal to (Q+ - Q-)/Q+. Heat loss during the combustion process reduces Q+. Heat loss during expansion process increases reduces Q-. Thermodynamic analysis of a reciprocating engine performance can be limited to combustion and expansion processes. The rest of processes are for logistics to replenish cylinder with fresh charge. The necessary equations of the state to relate working fluid state at point 2 to that at point 1 are derived from idea gas law. Gases have various properties including the gas pressure p, temperature T, mass m, and volume V that contains the gas. If any two of the properties are fixed, the nature of the relationship between the other two is determined as follows. If the pressure and temperature are held constant, the volume of the gas depends directly on the mass. If the mass and temperature are held constant, the product of the pressure and volume is a constant (Boyle’s Law). If the mass and pressure are held constant, the volume is directly proportional to the temperature (Charles’ law). By combining these two laws, pV/T is always a constant when work is done on or by the gas or heat is transferred into or from the gas, as the gas going through a thermodynamic process. Because pV/T is always a constant, the equation p2V2/T2 = p1V1/T1 is true in every instance including when all gas properties are in equilibrium. Therefore, the equation p2V2/T2 = p1V1/T1 is an equation of the state to relate the gas properties in equilibrium at point 2 to that in equilibrium at point 1 so that the law of conservation of energy can be met. According to Dalton’s law, a gas mixture behaves in exactly the same fashion as a pure gas. Therefore, the equation of the state, p2V2/T2 = p1V1/T1, relates working fluid state at point 2 to that at point 1 regardless whether process 1-2 is isentropic or not. The pressure reaches equilibrium quickly and thus p2/p1 = (V1/V2)k can be taken as another equation of the state of working fluid. There two equations of the state of the working fluid can be used to compute the pressure p and the average temperature T of the working fluids in every instance. Because idea gas law is taught in high school physics, anybody having taken high school physics can understand how a reciprocating IC engine works and know how to improve it.
The existing automotive engines are designed by try and error without applying the thermodynamic principle. When thermodynamics is properly applied, a new automotive engine can be designed to achieve the maximum possible fuel efficiency with minimum emissions. It is illogical to give up the internal combustion engine simply because no good one has yet been developed.
The reciprocating internal combustion engine is a device to convert fuel chemical energy into mechanical work. Even though combustion taking place inside the cylinder, it is equivalent to combustion taking place out side the cylinder and the converted heat being transferred to the gas inside the cylinder. The heat so transferred is denoted by Q+. The ensuing expansion process converts a part of the thermal energy into mechanical work. The remaining part of the thermal energy is rejected from the cylinder at the end of expansion process. The heat transferred from inside the cylinder to the outside by the exhaust gas is denoted by Q-. By definition, the thermal efficiency is equal to (Q+ - Q-)/Q+. Heat loss during the combustion process reduces Q+. Heat loss during expansion process increases reduces Q-. Thermodynamic analysis of a reciprocating engine performance can be limited to combustion and expansion processes. The rest of processes are for logistics to replenish cylinder with fresh charge. The necessary equations of the state to relate working fluid state at point 2 to that at point 1 are derived from idea gas law. Gases have various properties including the gas pressure p, temperature T, mass m, and volume V that contains the gas. If any two of the properties are fixed, the nature of the relationship between the other two is determined as follows. If the pressure and temperature are held constant, the volume of the gas depends directly on the mass. If the mass and temperature are held constant, the product of the pressure and volume is a constant (Boyle’s Law). If the mass and pressure are held constant, the volume is directly proportional to the temperature (Charles’ law). By combining these two laws, pV/T is always a constant when work is done on or by the gas or heat is transferred into or from the gas, as the gas going through a thermodynamic process. Because pV/T is always a constant, the equation p2V2/T2 = p1V1/T1 is true in every instance including when all gas properties are in equilibrium. Therefore, the equation p2V2/T2 = p1V1/T1 is an equation of the state to relate the gas properties in equilibrium at point 2 to that in equilibrium at point 1. According to Dalton’s law, a gas mixture behaves in exactly the same fashion as a pure gas. Therefore, the equation of the state, p2V2/T2 = p1V1/T1, relates working fluid state at point 2 to that at point 1. The pressure reaches equilibrium quickly and thus p2/p1 = (V1/V2)k can be taken as another equation of the state of working fluid. These two equations of the state must be used for applying thermodynamics to the reciprocating internal combustion engines. National Research Council reviewed yearly progress reports of PNGV project for a decade without realizing that 80 mpg goal was impossible to reach. After spent two billions of dollars, the demised PNGV project was replaced by FredomCar project which will also fail because for both projects, thermodynamics has not been properly applied. National Research Council should recommend further reciprocating engine research by applying thermodynamics before suggesting high-risk projects.
The reciprocating internal combustion engine is a device to convert fuel chemical energy into mechanical work. Even though combustion taking place inside the cylinder, it is equivalent to combustion taking place out side the cylinder and the converted heat being transferred to the gas inside the cylinder. The heat so transferred is denoted by Q+. The ensuing expansion process converts a part of the thermal energy into mechanical work. The remaining part of the thermal energy is rejected from the cylinder at the end of expansion process. The heat transferred from inside the cylinder to the outside by the exhaust gas is denoted by Q-. By definition, the thermal efficiency is equal to (Q+ - Q-)/Q+. Heat loss during the combustion process reduces Q+. Heat loss during expansion process increases reduces Q-. Thermodynamic analysis of a reciprocating engine performance can be limited to combustion and expansion processes. The rest of processes are for logistics to replenish cylinder with fresh charge. The necessary equations of the state to relate working fluid state at point 2 to that at point 1 are derived from idea gas law. Gases have various properties including the gas pressure p, temperature T, mass m, and volume V that contains the gas. If any two of the properties are fixed, the nature of the relationship between the other two is determined as follows. If the pressure and temperature are held constant, the volume of the gas depends directly on the mass. If the mass and temperature are held constant, the product of the pressure and volume is a constant (Boyle’s Law). If the mass and pressure are held constant, the volume is directly proportional to the temperature (Charles’ law). By combining these two laws, pV/T is always a constant when work is done on or by the gas or heat is transferred into or from the gas, as the gas going through a thermodynamic process. Because pV/T is always a constant, the equation p2V2/T2 = p1V1/T1 is true in every instance including when all gas properties are in equilibrium. Therefore, the equation p2V2/T2 = p1V1/T1 is an equation of the state to relate the gas properties in equilibrium at point 2 to that in equilibrium at point 1. According to Dalton’s law, a gas mixture behaves in exactly the same fashion as a pure gas. Therefore, the equation of the state, p2V2/T2 = p1V1/T1, relates working fluid state at point 2 to that at point 1. The pressure reaches equilibrium quickly and thus p2/p1 = (V1/V2)k can be taken as another equation of the state of working fluid. These two equations of the state must be used for applying thermodynamics to the reciprocating internal combustion engines. National Research Council reviewed yearly progress reports of PNGV project for a decade without realizing that 80 mpg goal was impossible to reach. After spent two billions of dollars, the demised PNGV project was replaced by FredomCar project which will also fail because for both projects, thermodynamics has not been properly applied. National Research Council should recommend further reciprocating engine research by applying thermodynamics before suggesting high-risk projects.