Controlled temperature combustion engine

Details Controlled temperature combustion engine Controlled temperature combustion engine

2002-08-08

2003-11-25

Denion, Thomas (Department: 3748)

Power plants

Fluid motor means driven by waste heat or by exhaust energy...

With supercharging means for engine

C060S602000, C060S280000, C123S435000, C123S305000, C123S564000

Reexamination Certificate

active

06651432

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a reduction of NO
x
and PM emissions from combustion engines. The field of application is primarily in internal combustion engines for motor vehicles, but this invention can also be utilized in other energy conversion “engines” which utilize combustion of chemical fuels, including electric power generation plants.
2. The Prior Art
The growing use of motor vehicles greatly adds to the atmospheric presence of pollutants, such as oxides of nitrogen and particulate matter, and has created a demand for a significant reduction in such emissions.
Prior art gasoline engines generally operate with charge-air throttling and intake port fuel injection to provide a mixture of fuel and charge-air for inducting into the combustion chambers. The term “charge-air” as used herein means either air or a mixture of air and recirculated exhaust gas. Charge-air throttling is used to control the load (or torque) output of the engine and results in significant efficiency penalties, especially at lower loads. Port fuel injection is used to provide good control and mixing of the required fuel with charge-air. Pre-mixed fuel and charge-air will auto-ignite during compression, depending on the fuel and charge-air characteristics, at a certain compression ratio which corresponds to the auto-ignition temperature of the fuel and charge-air mixture. Prior art gasoline engines are generally limited to compression ratios of between 9:1 and 10:1 to avoid uncontrolled auto-ignition. The ignition process is initiated by the sparking of a spark-plug so that rapid combustion begins at or near piston top dead center TDC, (generally between TDC and 20 crank angle degrees after TDC), and combustion propagation proceeds from the ignition location as a “flame-front” traveling through the combustible mixture. At higher compression ratios and some operating conditions, the fuel and charge-air mixture auto-ignites in an uncontrolled manner and exhibits unacceptable “knock.” Not being able to safely operate at higher compression ratios significantly reduces the engine's efficiency potential.
some gasoline engines utilize direct fuel injection (fuel is injectec directly into the combustion chanber), with or without charge-air throttling. Generally, these engines operateat low loads throgh stratified combustion. The fuel is injected relatively late in the compression stroke with little or no charge-air throttling. A spark then initiates combustion that can occur as long as the stratified mixture is within the flamability limits of the fuel. Since the late injection allows less time for good fuel and charge-air mixing than pre-mix operation, such combustion is characterized by higher unburned fuel and particulate emissions. Also, localized temperatures are high and NO is formed and becomes part of the exhaust emissions. At higher loads the beginning of the fuel injection occurs earlier to allow more time for fuel and charge-air mixing. The earlier fuel injection limits the compression ratio for gasoline to levels comparable to the pre-mixed engines since in effect they become pre-mixed engines at high loads. Pre-mixed gasoline engines also experience high combustion temperatures and produce significant NO emissions.
Prior art diesel engines operate over all loads with late direct fuel injection and with little or no charge-air throttling. Diesel engines also operate at a relatively high compression ratio (generally between 15 and 20 to one) as compared to prior art gasoline engines because they make use of the auto-ignition properties of diesel fuel. Diesel fuel will under all intended operating conditions auto-ignite when injected into the compressed charge-air at or near TDC. As a result of these operating characteristics, diesel engines exhibit high efficiency. The primary problems with diesel engines are the unburned fuel, particulate and NO
x
emissions, as previously explained for late direct injection of gasoline. Gasoline could be used in prior art diesel engines by adding an assured source of ignition (e.g., a spark or glow plug), but still with the same emission problems.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide for both efficient engine operation and extremely low levels of NO
x
emissions.
It is another object of the present invention to provide a method of engine operation wherein compression temperature and peak combustion temperature are controlled over an engine's speed and load range.
Accordingly, the present invention provides a method of operation of an internal combustion engine including intaking ambient air through at least one compressor to provide a charge-air at a boosted pressure and introducing the boosted charge-air to the internal combustion engine. The method further includes introducing fuel into the internal combustion engine for combustion in admixture with the charge-air at a combustion temperature approximating a target value, producing an exhaust gas. Engine operating conditions, inclusive of torque demand, are sensed and the boosted pressure is changed proportional to a change in the sensed torque demand so as to maintain the combustion temperature at approximately the target value, which value is below 2100° K.
In a preferred embodiment the method further involves passing a portion of the charge-air through a heat exchanger with bypass of the heat exchanger by a second portion of the charge-air. The temperature of the charge-air is sensed downstream of the bypass line and heat exchanger and the amount of the second portion bypassing the heat exchanger is controlled by operation of a control valve in the bypass line to bring the sensed intake temperature to a target temperature determined in accordance with the sensed engine operating conditions.
A portion of the exhaust gas may be recirculated for admixture with the charge-air and fuel. In this case, oxygen concentration in the admixture is sensed and the amount of EGR is regulated to bring the sensed oxygen concentration to a target oxygen concentration determined for the sensed engine operating conditions. The fuel feed is controlled responsive to the sensed temperature of the charge-air intake and the sensed boost pressure.
The fuel may be introduced into the charge-air downstream or upstream of the compressor so that the fuel is contained within the charge-air.
Thus, the present invention provides, in an internal combustion engine, high compression ratio (e.g., generally greater than 15 to 1 in the compression stroke) operation with little or no charge-air throttling, as is characteristic of the high-efficiency diesel-cycle engine, but without the emission problems of prior art engines, through a unique, new method of operation.
The formation rate of the pollutant NO during the fuel combustion process can be generally expressed in simplified form as follows:
NO formation rate=C
1
[N
2
]
C
2
[O
2
]
C
3
exp
C
4
T
  (I)
Where: C
1
, C
2
, C
3
, and C
4
(C
x
) are constants, [N
2
] is the concentration of nitrogen, [O
2
] is the concentration of oxygen, exp is a constant, and T is the absolute temperature of the mixture.
Since temperature is an exponent in the above formula (I), it can be expected that for given concentrations of nitrogen and oxygen, the NO formation rate increases exponentially with temperature. This relationship is widely recognized and is shown graphically in
FIG. 1
for typical engine operating conditions. Engine combustion times general fall within one to five milliseconds. It can clearly be seen that the formation of NO will be minimal if the engine combustion temperature can be maintained below about 2000 degrees Kelvin(K). The desirability of maintaining combustion temperatures below this level and yet still have combustion rapid enough to be complete for practical engine speeds, is well known. A recent Society of Automotive Engineers Technical Paper (#2000-01-1177) by Patrick F. Flynn and others from Cummins E

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