Aug. 24, 1965 W. G. LOVELL 3,202,141 METHOD OF OPERATING COMPRESSION IGNITION ENGINE Original Filled Oct. 27, 196 44 42 t - 40 - -m-m- -- -- - 38 -l L B 36 /, | | 34. | 32 - - - -- |- - C 3O |- | H- --- 28 f 1. D A, FullDiesel 26 + - B,C. PropaneNatural Gas Pius Plus Tetramethylead Tetramethyl lead D. Propane Plus Tetraethyl lead 24 H 22 O 2 3. 4 5 6 LEAD, GRAMS PER THERM OF PRIMARY FUEL INVENTOR. WHEELER G. LOWELL BY 3,202,4 United States Patent Office Patented Aug. 24, 1965 2 in shock loading of pistons, bearings, and other engine 3,202,141 METHOD OF OPERATING COMPRESSION parts as well as loss in power output. To avoid this loss IGNITION ENGINE of combustion control, engine manufacturers have had to Wheeler G. Lovell, Bloomfield, Mich., assignor to Ethyl limit the power output of the engine. This is accom Corporation, New York, N.Y., a corporation of 5 Virginia plished by reducing the amount of primary fuel intro Continuation of application Ser. No. 148,277, Oct. 27, duced into the combustion chamber during each cycle 1961. This application July 1, 1963, Ser. No. 295,585. which in turn results in lower power output. 6 Claims. (Cl. 123-1) The fact that the use of certain gaseous fuels in a 10 dual fuel operation results in loss of combustion control This application is a continuation of application serial has long been recognized. As far back as 1898, Rudolph No. 148,277, filed October 27, 1961, which, in turn, is a continuation-in-part of pending applications Serial Num Diesel recognized this problem. In his British Patent bers 11,416 and 11,417, both filed February 29, 1960, all No. 7,657 claiming the method of operating an internal of which are abandoned. 5 combustion engine on a dual fuel cycle, he stated that he This invention relates to a method of operating an in could use "illuminating gas . however only in small ternal combustion engine. More particularly, the inven proportion to the air.” In other words the amount of tion relates to an efficient and economical operation of fuel had to be reduced or limited to retain combustion diesel engines adapted to operate on a dual fuel cycle. 20 control. Thus, for a period of over 60 years, this problem For the purpose of this invention, dual fuel engines are of loss of combustion control when using a dual fuel cycle defined as compression ignition engines which use as a has plagued the industry. The problem has not been portion of the fuel supply, a normally gaseous material solved but only circumvented by accepting the penalty of (hereinafter also referred to as the primary fuel), such as limiting the power output of the engine to avoid the prob natural gas, liquefied petroleum gas, methane, ethane, 25 lems associated with combustion control loss. propane, etc. Ignition of the gaseous primary fuel is ac It is an object of this invention to provide a method of complished by the injection of a charge of diesel fuel operating a dual fuel engine in an economical and efficient (hereinafter also referred to as pilot charge) into the com manner. Another object is to provide a method whereby 30 the power output available from a dual fuel engine is pressed gas mixture. Thus, normal dual fuel operation equal to or greater than the maximum power available comprises induction of a primary fuel-air mixture into when operating under full diesel conditions. the combustion chamber, compressing this mixture by It has now been found that surprisingly, a material means of the compression stroke, and at some point dur normally used as an antiknock agent in gasoline fuels for ing the compression stroke, injecting a pilot charge of 35 diesel fuel into the compressed primary fuel-air mixture. spark-ignited engines can be used as a combustion con The pilot charge of diesel fuel is injected through a con trol improver in compression ignition engines operated on ventional diesel fuel injection system and acts as a source a dual fuel cycle. Accordingly, the objects of this inven of ignition for the compressed fuel-air mixture. In nor tion are accomplished by the method of this invention mal dual fuel operation, air to the engine is not throttled which method comprises the steps of: but is constant. Power output from the engine is con (1) Introducing into the combustion chamber of a trolled by varying the amount of gaseous fuel admitted compression ignition engine a gaseous fuel, an organome into the combustion chamber. For a given engine, the tallic combustion control additive, and air to form a com quantity of the pilot charge of diesel fuel per cycle is usual 45. bustible mixture, said combustion control additive being ly fixed, regardless of engine output. At full load the present in an amount such that the metal is present in a amount of the pilot charge usually represents less than 10 concentration of from 0.001 to about 0.5 weight percent percent of the total fuel to the engine. based on the weight of said gaseous fuel, One of the main incentives for using a dual fuel cycle (2) Compressing said mixture to about from 42 to is economy. Many widely available gaseous fuels are 50 about 42 of its original volume so as to be at a tempera much cheaper than conventional diesel fuel. Moreover, ture sufficient to ignite diesel fuel, using gaseous fuels allows smoother, cleaner combus (3) Injecting into the combustion chamber a pilot tion with a minimum of combustion chamber deposits. charge of diesel fuel so as to initiate combustion of the Engine maintenance costs are reduced and engine life is 55 total mixture, the weight ratio of said pilot charge to said prolonged. gaseous fuel being from about 0.01:1 to about 1:1, said In many instances operating a compression signition pilot charge optionally containing from about 0.001 to engine on the dual fuel cycle results in a severe penalty, about 1 percent of combustion control additive. for only a fraction of maximum power is available as The combustion control additives of this: invention compared with operating the engine as a full diesel. The 60 comprise compounds selected from the group consisting sharp reduction in power output is due to a loss of com of organo-lead compounds and a hydrocarbon soluble bustion control. This loss of combustion control is organometallic compound of a metal of atomic number evidenced by rough operation, audible noises, combustion The above-enumerated combustion control additives knock, etc. This is very objectionable for it results 65 25-28 inclusive. 3,202,141 3. 4. may be added singly or in any combination to the gaseous with those of the blend and a cetane number is according primary fuel-air mixture. In some situations, it is also ly assigned to the diesel fuel. desirable to add a combustion control additive to the With spark-ignited internal combustion engines, the diesel pilot charge. In any event, in the practice of this primary fuel characteristic is octane number. This is invention, a combustion control additive as described 5 the measure of the ability of a fuel to resist pre-spark or above must be present in the gaseous primary fuel-air mix uncontrolled and erratic combustion. As with diesel fuel, ture. In a preferred method, a relatively volatile additive the end objective is to control combustion so as to obtain is added to the gaseous primary fuel and a second, heavier a smooth, even pressure rise. The term designating this additive which may produce a synergistic effect is added quality is known as octane number. The resistance of the to the diesel pilot charge. A specific example is to add O fuel to pre-flame combustion, uncontrolled combustion, tetramethylead to the primary fuel and methylcyclopen etc. usually known as knock, is compared with that of iso tadienyl manganese tricarbonyl to the pilot charge. octane, the top of the scale, and n-heptane, the bottom of The inclusion of a material normally used as an anti the scale. A single-cylinder engine is operated in accord knock material in the gaseous primary fuel permits much ance with the standard ASTM procedure and the anti greater power to be developed than heretofore possible. knock quality of the fuel is matched with that of a blend By the use of the method of this invention, combustion of isooctane and heptane. The percentage of isooctane control is retained, allowing operation of the dual fuel in the blend having the same antiknock properties as those engine in a manner so as to obtain as much and oftentimes of the fuel is assigned as the fuel octane number. The more power than that possible when operating the engine higher the octane number the more desirable the fuel. as a full diesel. This is surprising for the art has long 20 Thus, with normal diesel fuel operation, in order to recognized that organometallic antiknock materials such retain combustion control, the desirable fuel quality is as tetramethylead, although useful in gasoline fuels used ability to ignite within a fairly short time, whereas with for spark-ignited engines, were not useful but in some spark-ignited engines the desirable fuel quality is ability respects even harmful when included in diesel fuel. In to resist combustion until ignited by the spark. From order to understand the import of this statement, it is nec 25 these considerations it would be expected, and the art rec essary to consider the diesel combustion process. ognizes, that a good diesel fuel would make a poor fuel In diesel operation combustion control is mainly ob for spark-ignited engines and vice-versa.