Stratified Charge Spark Ignition Internal Combustion Engine With Exhaust Recycle

Abstract

A spark ignition system and a method for operating same by passing a first fuel-air mixture into a precombustion chamber of the engine and a second leaner fuel-air mixture into a primary combustion chamber, igniting the first mixture for igniting the second mixture, and controllably mixing about 5 to about 20 percent of the exhaust gas resulting from the combustion of the fuel mixtures with the second fuel-air mixture during operation of the engine at greater than about 75 percent maximum power output with the amount of exhaust gas being mixed with the second fuel-air mixture varying directly with the power output of the engine.

Description

It is desirable to provide a spark ignition system which will operate with low pollution emissions while maintaining high power output and efficiency.

This invention therefore resides in a spark ignition system and a method of operating same by passing a first fuel-air mixture into a precombustion chamber of the engine and a second leaner fuel-air mixture into a primary combusiton chamber, igniting the first mixture for igniting the second mixture, and controllably mixing about 5 to about 20 percent of the exhaust gas resulting from the combustion of the fuel mixtures with the second fuel-air mixture during operation of the engine at greater than about 75 percent maximum power output with the amount of exhaust gas being mixed with the second fuel-air mixture varying directly with the power output of the engine.

Other aspects, objects, and advantages of the present invention will become apparent from a study of the disclosure, the appended claims, and the drawings.

The drawings are diagrammatic views of the apparatus and data of tests performed on the apparatus. FIG. 1 shows the apparatus of this invention, FIG. 2 shows the combustion chambers, FIG. 2a shows element 6 in more detail and FIGS. 3-8 show data of tests performed on the engine.

Referring to FIGS. 1 and 2, a spark ignition engine 2 has a primary combustion zone 4 and a precombustion zone 6 that are in fluid communication one with the other. For simplicity, reference will be made to the primary and precombustion zones in the singular. It should be understood, however, that the engine can have a plurality of primary combustion zones, preferably with each primary zone having a precombustion zone with the associated elements as set forth with reference to the singular zones.

Each of the combustion zones 4, 6 has a separate carburetor 8, 10 connected in fluid communication therewith which in turn is connected to an air supply, a fuel supply, and a throttle for controllably discharging fuel-air mixtures from the carburetors 8, 10 into their respective combustion zones 4, 6.

The carburetor 8 of the primary combustion zone or chamber 4 is constructed to receive and mix fuel and air therein and discharge a fuel-air mixture into the primary combustion zone 4 that is a relatively lean fuel-air mixture, being less than about an 80 percent stoichiometric fuel.

The carburetor 10 of the precombustion zone or chamber 6 is constructed to receive and mix fuel and air therein and discharge a fuel-air mixture into the precombustion chamber 4 that is a richer mixture relative to the other fuel mixture, preferably a fuel-air mixture in the range of about a 500 to about a 1,000 percent stoichiometric fuel.

A spark ignition system, generally referred to by numeral 12, is associated with the precombustion chamber 6 for igniting the fuel-air mixture therein, which in turn ignites the fuel-air mixture in the primary combustion zone 4 for operating the engine 2.

An exhaust conduit 14 (FIG. 1) is connected to the exhaust outlet of the primary combustion chamber 4 for directing the exhaust gas resulting from combustion of the first and second fuel-air mixtures from the engine 2.

An exhaust gas recirculating conduit 16 is connected in fluid communication with the primary combustion zone 4 and the exhaust conduit 14.

A measuring means, for example a pressure controller 18, is associated with the engine 2 for measuring a variable representative of the power output of the engine 2 and delivering a signal representative thereof. For example, the measuring means can measure the intake manifold pressure of the primary combustion zone 4 as shown in FIG. 1.

A control means, such as a control valve 20 for example, is positioned in the exhaust gas recirculating conduit 16 and is connected to the measuring means 18 for receiving a signal therefrom and opening and closing the valve in response to said signal. The valve 20 is constructed to be in the closed position in response to a signal representative of the output of the engine being less than about 75 percent maximum power output of the engine. The valve 20 is open and controllably positioned in response to a signal from the measuring means representative of the output of the engine 2 being greater than about 75 percent maximum power output with the opening of said valve 20 varying directly with the power output of the engine 2 and passing exhaust gas in the range of about 5 to about 20 percent of the total exhaust gas passing through conduit 14.

FIGS. 3-8 show the results of tests on an engine of this invention.

The precombustion chamber used in these tests had the following characteristics:

Shape: cylindrical

Orifice: one-eighth in. square edge

Volume: 0.83 cu. in.

Intake valve location: rear of chamber

Spark gap location: rear of chamber

Length/Diameter: 3.80

The precombustion chamber was operated with a supply of fuel-air mixture such that 88 percent of the precombustion chamber volume was filled with mixture at the beginning of the compression stroke. Fuel was present in the mixture supplied the precombustion chamber in an amount 5 times that required for a stoichiometric mixture, i.e., 500 percent stoichiometric fuel.

The engine used was a CFR, single cylinder unit similar in basic configuration to the standard knock-test engine except for two additional combustion chamber access holes. A sketch of the arrangement of the precombustion chamber and the main CFR engine combustion chamber is shown in FIG. 2. The fuel was a conventional premium grade gasoline having a research octane number of 99 and containing 2.5 ml TEL per gallon.

In lieu of an acceptable technique for the direct measurement of noise, the effect of exhaust gas recirculation (EGR) to reduce noise was documented in terms of the peak value of the first time-derivative of cylinder pressure. The filtered output of the standard D-1, magnetostrictive knock-test pickup furnished the dP/dT signal. FIG. 3 presents peak dP/dT values on an arbitrary, but linear, scale as functions of stoichiometry. Results of the conventional engine, the precombustion chambered engine, and the precombustion chambered engine with 8 percent EGR are included. Objectionable combustion noise did not occur below a value of 6 on the scale in FIG. 3. Thus, the data in that Figure showed that 8 percent EGR in the precombustion chambered engine extended noise-limited operation to 103 percent stoichiometric fuel from 89 percent with no EGR. This is judged to be a significant expansion of the useful operation range of the precombustion chambered engine.

FIG. 4 presents exhaust NO.sub.x concentrations (as NO) plotted against the percentage stoichiometric fuel. At all stoichiometries richer than 70 percent stoichiometric fuel, 8 percent EGR reduced NO.sub.x emission. At stoichiometrics leaner than 70 percent, the presence of recirculated exhaust gas appeared to increase NO.sub.x. Although the reasons for this increase are unknown, it is unimportant since NO.sub.x values with the prechambered engine were quite low at the stoichiometries where the increase occurred. Hence, there would be no incentive for EGR application in this stoichiometry range. Eight Percent EGR reduced NO.sub.x from the precombustion chambered engine about 54 percent at 90 percent stoichiometric fuel at constant power.

FIG. 5 shows that 8 percent EGR in the precombustion chambered engine produced a 4 to 7 percent loss of power at constant throttle. The prechambered engine without EGR resulted in a 5 to 9 percent decrease in power as compared to the conventional engine. The total power decrease attributed to the simultaneous application of the precombustion chambered combustion process and the 8 percent EGR was about 12 percent. Although not desirable, this power loss is certainly acceptable.

FIG. 6 shows that 8 percent EGR had only a mirror effect on exhaust hydrocarbon concentrations. From 100 percent to 70 percent stoichiometric fuel, which is the range where EGR is applied to the precombustion chambered engine, 8 percent EGR increased hydrocarbon emissions no more than 14 percent and as little as 6 percent.

FIG. 7 shows that the influence of 8 percent EGR on the carbon monoxide emissions from a precombustion chambered engine is negligible.

FIG. 8 compares the effectiveness of about the same amount of exhaust gas recirculation (EGR) on NO formation from a conventional engine and a prechambered engine. This figure shows that applying EGR to the prechambered engine has about the same benefit on NO (at a given stoichiometric mixture) as the application of EGR to the conventional engine. However, with the conventional engine, the application of EGR enrichens the lean misfire limit from about 74 percent stoichiometric fuel to about 89 percent stoichiometric fuel (see FIG. 8) which limits the usefulness of EGR. With the prechambered engine, the application of EGR has no deleterious effect on lean misfire limit. In addition, EGR has the other important benefit of substantially reducing excessive rates of pressure rise (leading to noise) of the prechambered engine.

This invention therefore provides a spark ignition engine which will operate with low pollution emissions while maintaining high power output and efficiency.

Other modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing discussion and accompanying drawings, and it should be understood that this invention is not to be unduly limited thereto.

Claims

1. A method for operating a spark ignition engine having a precombustion chamber in communication with a primary combustion zone and means for igniting a fuel-air mixture in the precombustion chamber, comprising:

controllably passing a first fuel-air mixture into the precombustion chamber;

controllably passing a second fuel-air mixture into the primary combustion zone, said second fuel-air mixture being a leaner fuel mixture relative to the first mixture;

igniting the first mixture in the precombustion zone for igniting the second mixture in the primary combustion zone; and

controllably mixing about 5 to about 20 percent of the exhaust gas resulting from the combustion of the first and second fuel-air mixtures with the second fuel-air mixture during operation of the engine at greater than about 75 percent maximum power output of the engine, said amount of exhaust gas being mixed with the second fuel-air mixture varying directly

2. A method, as set forth in claim 1, wherein the first fuel-air mixture is in the range of about a 500 to about a 1000 percent stoichiometric fuel.

3. A method, as set forth in claim 1, wherein the second fuel-air mixture

4. A method, as set forth in claim 3, wherein the first fuel-air mixture is in the range of about a 500 to about a 1,000 percent stoichiometric fuel.

5. In a spark ignition system having a primary combustion zone, mixing means for controllably mixing a primary fuel-air mixture, and means for passing said primary fuel-air mixture into the primary combustion zone, the improvement comprising:

a precombustion chamber being in fluid communication with the primary combustion zone;

mixing means for controllably mixing another fuel-air mixture being a richer fuel mixture relative to said primary fuel-air mixture;

means for passing said other fuel-air mixture into the precombustion chamber;

means for igniting the fuel-air mixture in the precombustion chamber for igniting the primary fuel-air mixture in the primary combustion zone;

exhaust means for directing the combustion gas resulting from combustion of the fuel-air mixture from the engine;

measuring means for measuring a variable representative of the power output of the engine and delivering a signal in response thereto;

a conduit connected in fluid communication with the exhaust means and the primary combustion chamber;

control means for passing about 5 to about 20 percent of the exhaust gas resulting from the combustion of the first and second fuel-air mixtures into the primary combustion chamber during operation of the engine at greater than about 75 percent maximum power output of the engine, said control means comprising a control valve positioned in the conduit and connected to the measuring means, said valve being in a closed position in response to a signal from the measuring means representative of the output of the engine being less than about 75 percent maximum power output and said valve being controllably opened in response to a signal from the measuring means representative of the output of the engine being greater than about 75 percent maximum power output with the opening of said valve

6. An apparatus, as set forth in claim 5, wherein the variable measured by the measuring means is the manifold pressure of the primary combustion

7. An apparatus, as set forth in claim 5, wherein the mixing means for the primary fuel-air mixture is a carburetor adapted to provide a fuel-air

8. An apparatus, as set forth in claim 5, wherein the mixing means for the other fuel-air mixture is a carburetor adapted to provide a fuel-air mixture in the range of about a 500 to about a 1,000 percent

9. An apparatus, as set forth in claim 8, wherein the mixing means for the primary fuel-air mixture is a carburet0r adapted to provide a fuel-air mixture less than about an 80 percent stoichiometric fuel.