This invention relates to internal combustion engines, and more particularly to using passive pre-chamber ignition with such engines.
The pre-chamber ignition concept is used with spark-ignition engines to enable lean or diluted engine operation while having a suitable combustion process. The basic function of a pre-chamber is to provide a small space where fuel can be combined with air to form a mixture consistently ignitable by a spark plug. When ignited, this mixture provides the required energy to combust a lean or dilute mixture within the cylinder's main combustion chamber at the optimum time for efficiency and/or pollution control.
Various types of pre-chamber configurations exist, which can be classified into active and passive configurations. An active pre-chamber system is equipped with additional fuel and/or air injection inside the pre-chamber. A passive pre-chamber realizes its gas exchange by local flow fields near orifices into the main chamber and by pressure differences between the pre-chamber and main-chamber.
A passive pre-chamber spark plug is composed of an ordinary spark plug with electrodes, on which a cap with orifices is put. The encapsulated volume is the pre-chamber and is connected to the main combustion chamber by the orifices.
In addition to lean-burn natural gas engines, passive pre-chambers are attractive to improve the robustness of combustion in dilute mixture (high EGR) gasoline engines, as well as for increased burning rate in stoichiometric and rich gasoline engines.
A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:
The following description is directed to passive pre-chambers for spark-ignited engines. The pre-chamber's nozzles (orifices) are varied in size, rather than being all the same size. This improves scavenging while maintaining the original objectives of pre-chamber ignition.
The pre-chamber 100 is a bowl-shaped housing that surrounds the electrode end of sparkplug 11. The pre-chamber 100 is installed such that it communicates with the main chamber 10 of the combustion cylinder via orifices (herein referred to as “nozzles”) 22 and 23. The pre-chamber housing is made from a metal or other material that will withstand engine conditions, and is permanently attached to the end of spark plug 11 to form a sealed pre-chamber compartment.
During the engine's intake stroke, the pre-chamber nozzles 22 and 23 scavenge the residual in the main chamber 10 with fresh mixture from the intake flow. During compression, fresh mixture from the larger main chamber volume is forced through the nozzles 22 and 23 into the pre-chamber. When the sparkplug 11 ignites this mixture, burning jets expand through each nozzle 22 and 23, back into the main chamber. The result is multiple ignition points in the main chamber, providing a faster and more robust combustion event.
A feature of the invention is the recognition of engine conditions at which it is difficult to maintain reasonable performance of the passive pre-chamber concept. Under high load conditions, passive pre-chambers have been found to work very well. The mixture in the pre-chamber is easily ignited, and a burning jet exiting each nozzle provides multiple ignition sources in the main combustion chamber. The 10-90 burn duration (time or crank angle increment during which the tenth percentile to the ninetieth percentile of fuel is burned) is reduced to nearly half the duration seen under the same conditions in an open chamber engine.
However, at light loads and high dilution ratios, it is difficult to achieve ignition, much less complete combustion. The difficulty is explained by the inability to sufficiently evacuate the pre-chamber of the burned mixture from the previous cycle and low turbulence. A high percentage of the mass in the pre-chamber at the time of the spark event is burned exhaust gas. This dilutes the fresh mixture to the point that it will not ignite, or if it ignites the flame front is not sustained. Low turbulence slows down the flame propagation within the pre-chamber.
The view of
Referring to both
Based on bulk flow field and pre-chamber turbulence analyses, one or more of the nozzles between the pre-chamber and main chamber is made larger. This facilitates removal of residual from the pre-chamber while still creating a flame jet at each nozzle.
In the embodiment of
In the embodiments of
In the embodiment of
Each of the configurations shown in
The residual percentage in the pre-chamber is plotted during the late portion of the compression stroke. The dropping residual percentage is an indication of the burned gas being evacuated from the pre-chamber and replaced with fresh air-fuel mixture. For the case shown, complete evacuation would take the EGR percentage to 31% which is equal to the total (external+internal) EGR percentage inside the main chamber.
The top two plots are of two different pre-chambers having seven nozzles of the same diameter. The bottom two plots are of two pre-chambers with differently sized nozzles, such as those of
For the configurations of
This case is a divisional of U.S. application Ser. No. 16/866,256, filed May 4, 2020, and entitled “Passive Pre-Chamber Ignition with Varying Nozzle Sizes For Internal Combustion Engine”.
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20130055986 | Tozzi | Mar 2013 | A1 |
20140165980 | Cheira | Jun 2014 | A1 |
20140261296 | Sotiropoulou | Sep 2014 | A1 |
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Number | Date | Country |
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10 2014 004943 | Feb 2015 | DE |
10 2017 009228 | Apr 2019 | DE |
3 180 504 | Jun 2017 | EP |
2018 131911 | Aug 2018 | JP |
WO 2012091739 | Jul 2012 | WO |
Entry |
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Written Opinion of the International Searching Authority PCT/US2021/030372. |
Number | Date | Country | |
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20220170410 A1 | Jun 2022 | US |
Number | Date | Country | |
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Parent | 16866256 | May 2020 | US |
Child | 17592746 | US |