Internal-combustion engines – Convertible cycle
Reexamination Certificate
2001-12-17
2003-09-09
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Convertible cycle
C123S02700A, C123S316000
Reexamination Certificate
active
06615771
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of operating a direct injection internal combustion engine operated on both spark-ignitable and autoignitable fuel, more specifically on gasoline, wherein the operational range of the engine is allocated autoignition ranges and spark-ignition ranges, an at least nearly homogeneous fuel-air mixture being produced in the combustion chamber in autoignition ranges, a high compression ratio suitable for spontaneous ignition of the fuel being provided, the combustion in the autoignition range being mostly initiated by spontaneous ignition, and wherein in the ranges of spark ignition, combustion is initiated by spark ignition of said air-fuel mixture and a spark ignition range is assigned to the full load range and wherein an autoignition range is assigned to at least part of the part load range and the effective compression ratio is lowered in spark ignition ranges and combustion controlled by regulating the residual gas content in the ranges of spontaneous ignition.
DESCRIPTION OF PRIOR ART
The publication entitled “Homogeneous Charge Compression Ignition (HCCI) of Diesel Fuel”, Allen W. Gray et al., SAE Paper No. 971676 discloses that extremely low NO
x
and soot emission values are obtained during combustion of an auto-ignited lean fuel-air mixture on account of the homogeneous distribution of concentration and temperature. This process is known as HCCI combustion (
H
omogeneous
C
harge
C
ompression
I
gnition). It is also known that, on account of its high ignition property, diesel fuel is compounding the difficulty of carrying out this combustion process because the time of ignition can be fixated as desired just before top dead center only when the compression ratio and the effective medium pressure are low. As compared to conventional diesel processes, the low compression ratio required, which is of about 10, results in considerable disadvantages regarding the specific fuel consumption and the achievable power consumption, said disadvantages having heretofore prevented this combustion process from being more widely used although it yields favorable emission ratings. Another difficulty that is specific to diesel fuel is the position of the boiling range between approximately 170° C. and 360° C. that hinders evaporation and accordingly homogenization of the cylinder charge and that may yield high NO
x
, soot and unburned hydrocarbon emissions and involves the risk of diesel fuel mixing with the lubricant.
For HCCI combustion, gasoline presents great advantages on account of its low autoignition quality and the lower gasoline boiling range of between approximately 30° C. and 190° C. Analogous to the diesel engine, the compression ratio may here be raised to values of about 15 to 17. However, and as indicated in the publication entitled “An Experimental Study on Premixed-Charge Compression Ignition Gasoline Engine”, Taro Aoyama et al., SAE Paper No. 960081, the achievable effective medium pressure is again limited to the part load range, which represents a drawback.
Furthermore, German Pat. No. DE 36 32 579 C2 discloses an internal combustion engine operating on spark ignition and air compression at a compression ratio similar to that of a diesel engine in which the charge is stratified to ensure ignition of the air-fuel mixture. This stratified charge combustion may also be termed SCSI process (
S
tratified
C
harge
S
park
I
gnition). By applying the principle of charge stratification, the composition of the mixture in the range of the ignition source is made to lie within the limits of inflammability during spark discharge for a period that is long enough to allow a large enough flame to be produced to allow the cylinder charge to continue to burn. In the part load range however, such a stratified charge combustion, which relies on spark ignition, does not yield emission ratings that are as favorable as those of HCCI combustion, but it can be operated at much higher medium pressures and yields better soot emission ratings than the diesel engine.
The German Patent No. 28 51 504 A1 discloses a method of operating an internal combustion engine at a variable compression ratio, said internal combustion engine being operated on one kind of fuel for both spark ignition and spontaneous ignition. In this internal combustion engine, the compression ratio is increased in the part load range to carry out autoignition and is reduced in the full load range for spark ignition. For diesel operation, fuel is supplied through an injection nozzle discharging into the main combustion chamber or into a precombustion chamber, a non-homogeneous fuel-air mixture being produced in the combustion chamber as a result thereof. Accordingly, it does not operate on HCCI combustion principles. In one embodiment, the fuel for spark ignition operation is delivered by a carburetor and in another embodiment, it is supplied through an additional injection nozzle discharging into a secondary combustion chamber. In the spark ignition range, combustion is initiated by way of a spark plug ending in the secondary combustion chamber. In the spark ignition mode with fuel injection and air aspiration at full load, there is a charge concentration in the secondary combustion chamber relative to the main combustion chamber. Thanks to this known method, stable operational behavior and good efficiency may be achieved. Nevertheless, the ultra-low emission values known from the HCCI combustion cannot be achieved.
U.S. Pat. No. 4,126,106 A also describes an internal combustion engine which operates both under Otto cycle and on a diesel cycle. During starting and part load operation, a stratified charge is produced by injecting the fuel directly into the combustion chamber and combustion is initiated by spark ignition of this stratified charge. At full load, by contrast, the fuel is directly impinged into the combustion chamber on the hot walls thereof, the fuel evaporating and being ignited by compression according to the diesel combustion process as a result thereof. The engine thereby operates at a compression ratio of less than 16:1. During higher load of the motor however, the time between the start of the injection and the moment of spontaneous ignition is no longer sufficient to form a good mixture, which leads to a degradation of the combustion process and of emissions.
Furthermore, U.S. Pat. No. 3,125,079 A discloses a multi-purpose internal combustion engine that operates both by spontaneous ignition and by spark ignition at a fixed compression ratio of 15:1. The fuel is directly radially injected into the combustion chamber by way of a multi-apertured injection nozzle. This is not suited to produce a high degree of stratification of the charge.
In order to improve exhaust emission quality while keeping a high degree of efficiency on an internal combustion engine operating on spark ignited and on auto-ignited fuel, AT 003135 U suggests to produce, in the autoignition range, an at least nearly homogeneous fuel-air mixture in the combustion chamber. During high load of the engine, this method presents the advantages of HCCI combustion and avoids its drawbacks by shifting to spark ignition. The method thus combines the advantages of the HCCI process with those of the SCSI combustion. In order to permit the setting of a compression ratio that is higher in the part load range than in the full load range, a variable valve control system is provided by means of which the time for opening of at least one intake valve may be modified. The variable valve control system also causes the time for closing of at least one exhaust valve to be modified in function of the operational parameters of the motor so that the quantity of residual gas can be controlled to the effect of an internal exhaust recycling for the purpose of raising the temperature of the charge in the part load range.
An HCCI internal combustion engine must adjust its conditions of ignition to differential fuel properties, surrounding conditions and boundary conditions of the engine while respecting the
Denger Dirk
Fürhapter Alois
AVL List GmbH
Dykema Gossett PLLC
Salser Douglas A.
Wolfe Willis R.
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