专利汇可以提供Hybrid piston-pulsed detonation engine专利检索,专利查询,专利分析的服务。并且A hybrid piston engine-pulsed detonation engine structure is provided for obtaining shaft power from a pulsed detonation engine wherein a piston engine operatively connected to a PDE. A deflagration to detonation transition is used to achieve detonations. The piston engine has a piston that is located in the deflagration region of the deflagration to detonation transition. The hybrid engine has a critical starting frequency, above which the engine will self-actuate and produce excess power.,下面是Hybrid piston-pulsed detonation engine专利的具体信息内容。
This application claims priority of the filing date of Provisional Application Ser. No. 60/426,669 filed 12 Nov. 2002, the entire contents of which are incorporated by reference herein.
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
The present invention relates generally to pulsed detonation engines, and more particularly to a pulsed engine structure that provides shaft power.
In recent years, there has been a resurgence of interest and research directed toward pulsed detonation engines (PDE). Recent advances in computers and diagnostic tools have allowed researchers to overcome many of the technology hurdles hindering the construction of a practical PDE. Depending on the application, these obstacles include detonation initiation, valving or flow control, aspiration, power extraction and others. Traditionally, the PDE has been viewed as a thrust-producing engine, however, for the PDE to perform satisfactorily in most commercial applications, such as in commercial passenger jet airliners, a second engine for power extraction from the PDE would be required to run subsystems such as lights and air conditioning. A need exists in the art for a PDE that can generate both thrust power and shaft power.
It is therefore a principal object of the invention to provide an improved PDE.
It is another object of the invention to provide a PDE providing shaft power.
It is another object of the invention provide a modified piston engine-PDE providing both thrust and shaft power.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.
In accordance with the foregoing principles and objects of the invention, a hybrid piston engine-pulsed detonation engine structure is provided for obtaining shaft power from a pulsed detonation engine wherein a piston engine operatively connected to a PDE. A deflagration to detonation transition is used to achieve detonations. The piston engine has a piston that is located in the deflagration region of the deflagration to detonation transition. The hybrid engine has a critical starting frequency, above which the engine will self-actuate and produce excess power.
The invention will be more clearly understood from the following detailed description of representative embodiments thereof read in conjunction with the accompanying drawings wherein:
Experiments conducted on a hybrid piston-pulsed detonation engine to evaluate the power extraction characteristics may be found in the Provisional Application referenced above at the appendix entitled “Evaluation of a Hybrid Piston-Pulsed Detonation Engine,” AIAA 2002-0074, 40th Aerospace Sciences Meeting and Exhibit, Reno, Nev. (14–17 Jan. 2002).
Referring now to the drawings,
An electric motor was used as an external power supply to start the engine. A chain was used to connect the electric motor to the output sprocket of the transmission. With the transmission in gear and the clutch engaged, power from the electric motor was transmitted to the crankshaft and from the crankshaft (21 of
With spacer block 17 installed, the cam-chain and the oil supply and return lines to the head had to be extended. The spark and valve timing were altered from that of the stock engine. To maximize the power output of the hybrid engine the spark timing was adjusted so that the pressure from the detonation cycle occurred while the piston was traveling downward at maximum velocity. The valve and spark timing relative to the piston position is depicted in
By the time the piston reaches bottom dead center (BDC), the pressure and the remainder of the possible fire window was not used. At about 135° on the cam, exhaust valve 33 opens and purge air 34 (
In this particular embodiment the thrust of the hybrid engine was lower than that the thrust from a PDE alone. The volume of cylinder 11 was approximately 10% of detonation tube 13. Removing all of the work from the higher-pressure gas prior to blow-down would ideally decrease pressure in detonation tube 13 by about 14.4%. However, in this particular embodiment the thrust produced by the hybrid engine was about ½ that of the thrust on a PDE alone. The pressure of the shock wave traveling down detonation tube 13 was 2.6 times greater for the PDE alone. The blow-down pressure for the PDE was about 20% higher than that of the hybrid engine. In the hybrid piston-PDE the DDT was occurring as piston 20 was receding creating an expansion wave and hindering the DDT process, accounting for the difference in thrust between the two engines.
A deflagration to detonation transition (DDT) is used to achieve detonation. A Shelkin shocking spiral or other suitable detonation initiation mechanism can be used to transmission the deflagration to a detonation. Piston 20 is located in the deflagration region of the DDT, such that it is subject to the gradual rise of P3 detonation pressures, as opposed to the von Neumann shock.
Preferably, the valving arrangement 31, 33 for the piston engine will have ample valve area, such as a rotary, piccolo or slide valve. Traditional piston engines act as air pumps, since the motion of the piston in concert with the valve train can be used to draw in fresh air and expel exhaust products. However, in the present invention the piston cannot be used to pump air since the down stream end 15 of detonation tube 13 and hence of cylinder 11 are always open to the atmosphere. Thus, a means 36 (
The hybrid engine has critical starting frequency, therefore an external power source in necessary to achieve the critical frequency. Above this frequency the engine will self-actuate and produce excess power. Below this frequency, the power produced is less than that required to self-actuate and the engine decelerates and stops rotating. The critical frequency for this hybrid engine is a result of the different time constants for the piston movement and the detonation tube blow down event. The time constant for the piston engine is defined as,
tp=2/fcrank (1)
where fcrank is the frequency of the crankshaft 23 and the time constant for the blow down event is the time required for the pressure in the detonation tube 13 to decrease to ⅓ of the gage pressure behind the detonation wave. As a result, the pressure in cylinder 11 closed-end region reduces to be lower than that of the surrounding atmosphere. This low-pressure condition inside detonation tube 13 is detrimental to propulsion. Thus, a means to purge detonation tube 13 is preferred. One way to accomplish purging would be to insert inert gas through the exhaust valve before the start of another detonation cycle.
The rotational frequency of the hybrid engine can be governed in several ways. First, by reducing the fill fraction of detonation tube 13, which can be accomplished by altering the pressure in the intake manifold upstream of valves 31, 33. Second, the equivalence ratio of the charge can be used to govern the hybrid engine. Third, spark plug 25 timing can be altered. There is an optimum-spark-timing for extracting power from detonation. By moving the spark off this optimum timing, less work is extracted from the detonation, which will control the rotational speed off the engine, and generate more thrust. Finally, detonation tube 13 can be used to govern the rotational speed of the engine. Detonation tube length, instillation of a nozzle on the downstream end 15 of detonation tube 13 and the geometry of that nozzle can affect the blow-down time, which affects the amount of work and thrust that is extracted by the pistons 20.
For most of the conditions tested the time constant of the detonation-tube-blow-down was smaller than that of piston 20 movement. If the time constants were too different, the blow down process would occur while piston 20 would effectively be stationary; therefore little or no PdV work would be extracted from the detonation pressure. By increasing the starting frequency, and lengthening detonation tube 13, the time constants of the piston movement and blow down process were similar enough that the work extracted by piston 20 exceeded the requirement to self-actuate.
Referring now to
The ideal thermodynamic piston-PDE cycle consists of a constant volume heat addition process followed by an isentropic expansion process. In
The thermal efficiency 77 of the hybrid piston-PDE is given by:
Where γ is the ratio of specific heats and T is temperature.
The invention therefore provides a pulsed detonation engine system structure for producing shaft power from a PDE. It is understood that modifications to the invention may be made as might occur to one with skill in the field of the invention within the scope of the appended claims. All embodiments contemplated hereunder that achieve the objects of the invention have therefore not been shown in complete detail. Other embodiments may be developed without departing from the spirit of the invention or from the scope of the appended claims.
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