DESCRIPTION METHOD OF PRODUCTION OF SINTERED ORE AND SINTERING MACHINE TECHNICAL FIELD The present invention relates to a method of production of sintered ore for a blast furnace material and a sintering machine for the same. BACKGROUND ART The schematic steps in the conventional method of production of sintered ore will be explained using FIG. 1. First, iron-bearing material of the main material, iron ore, is fed out from an iron ore hopper, flux limestone is fed out from a limestone hopper, solid fuel coke is fed out from a coke hopper, returned ore (fine grained sintered ore smaller than a predetermined grain size for blast furnace use produced in the sintering process) is fed out from a returned ore hopper, and other materials are fed out from material hoppers 1 in predetermined amounts to form a sintering material 3. This is charged into one or more serially arranged mixers 2 and, in accordance with need, given water to adjust the moisture to 5.5% to 8.5% or so and granulated. Next, the granulated material of the sintering material 3 is charged once into a surge hopper 4, then the sintering material 3 is fed out from a drum feeder 5 and charged through chutes etc. into pallets forming the sintering machine so as to form a charged layer 7. The coke at the surface layer part of this charged layer 7 is ignited in an ignition furnace 8, then air is sucked from above the sintering material layer to below it while burning the coke in the sintering material. Due to this heat of combustion, the sintering material is successively sintered from the upper layer to the lower layer. The obtained sinter cake 9 is discharged at an ore discharge part, roughly crushed by a primary crusher 10, then cooled by a cooler 11. The cooled sintered ore is run through a primary sieve 12, secondary crusher 13, secondary sieve 14, tertiary sieve 15, etc. forming a crushing and grading process whereby approximately 5 mm or greater products are fed as finished sintered ore to the blast furnace. The less-than-approximately 5 mm sintered ore is mixed as returned ore with the sintering material and again charged into the sintering machine. FIG. 3 is a schematic explanatory view showing a descending state of a combustion zone in a sintering material layer and shows a vertical cross-section in the sintering machine strand direction, a vertical cross-section along the A-A cut section, a vertical cross-section along a B-B cut section, and a temperature distribution curve of the vertical direction (layer height). As shown in FIG. 3, in the sintering reaction of the upper layer of the sintering material layer, ordinary temperature air is sucked from above the sintering material layer to make the coke breeze in the sintering material layer burn, so a sharp temperature distribution with a low highest temperature and short high temperature holding time easily is formed. On the other hand, in the sintering reaction of the lower layer of the sintering material layer, ordinary and room temperature air passes through the sintering material layer during which time the heat of combustion of the coke breeze is used for preheating and other superior heat conditions are formed, so a broad temperature distribution with a high maximum temperature and a long high temperature holding time easily is formed. The difference in these firing temperatures has a direct effect on the ratio of formation of the liquid phase in the sintering reaction and is a factor governing the strength of the produced sintered ore and the product yield. An example of taking out sintering pallets at sintering completion positions in the sintering machine strand direction and measuring the yield distributions at different positions in the height direction and width direction in the sinter cake is shown in FIGS. 4. As shown in FIGS. 4(a) and (b), the yield at the upper layer (surface layer) of the sinter cake is 10% to 20% lower compared with the lower layer (grade surface). The phenomenon of the insufficient heat at this upper layer part is something which is in principle unavoidable for a down draft type sintering process. As prior art for dealing with this phenomenon of insufficient heat of the upper layer part, the method shown in Japanese Patent Publication (B2) No. 39-16754 (hereinafter referred to as "D1") has been proposed. D1 discloses the method of igniting the surface of the sintering material on the sintering machine, then spraying a liquid fuel of an oil to sinter the surface hard. This method uses heavy oil as liquid fuel and burns it together with the coke breeze at the top of the sintered layer after ignition to thereby deal with the insufficient heat at the upper layer part and improve the combustibility there. However, the art of spraying heavy oils shown in Dl has the three problems discussed next. The first problem is the limitation of the spraying positions of the heavy oil. Heavy oil and other oils are high in stickiness and low in volatility, so to make the sprayed heavy oil burn in the sintering machine, spraying it on a surface in a high temperature state right after ignition is essential. In a usual sintering machine, the surface of the sintering layer right after leaving the ignition furnace is rapidly cooled by the suction air. After approximately 1 minute (position of about 3 m from exit side of ignition furnace), it falls to 50°C or less. The general ignition point of heavy oil is 60 to 150°C. If spraying heavy oil on a low temperature surface of less than this ignition point, effective combustion cannot be expected. The majority of the oil is discharged unburned along with the sintered ore. Therefore, the spraying range of heavy oil in this art is restricted to the limited high temperature region right after the ignition furnace, so while this is effective for improvement of the strength of the uppermost layer part, free control of the sintering reaction at the middle layer and lower layer is difficult. The second problem is the risk of fire and in health and safety. If spraying heavy oil on a sintering surface at the exit side of the ignition furnace, fire and smoke are unavoidably produced along with the combustion of the heavy oil. In a usual sintering machine, air is sucked downward, but if spraying heavy oil, fire breaks out at the surface of the sintered layer. The heat causes an upward draft. At this time, black smoke containing soot is produced inside the sintering machine building, so separate installation of a hood and dust collection equipment in the spraying range of the heavy oil is essential from the viewpoint of health and safety and of fire prevention. Further, when poor ignition of the sintering surface etc. causes the surface temperature of the sintered layer to partially drop, the sprayed heavy oil is discharged unburned along with the sintered ore. In a usual sintering machine, intermixture of such a combustible material into the sintered ore is not envisioned, so it is necessary to study measures to deal with the risk of fire considering the possibility of leakage and buildup. The third problem is the increase in exhaust gas SOx. The oils obtained by fractionation of oil, in particular heavy oil, contain large amounts of sulfur, so the combustion exhaust gas includes a high concentration of SOx. The exhaust gas SOx of a sintering machine is strictly restricted by law in emission amount. When spraying heavy oil, there is the unavoidable problem of an increase of the emissions to more than the current levels. As prior art for dealing with these problems in the art of spraying heavy oil, there are the methods proposed in Japanese Patent Publication (A) No. 55-18585 (hereinafter referred to as "D2"), Japanese Patent Publication (A) No. 5-311257 (hereinafter referred to as "D3")/ and International Publication Pamphlet WO2007/052776 (hereinafter referred to as "D4"). D2 discloses the method of providing a hood over the sintering material layer at the front half part of the sintering machine in the strand direction, mixing combustible gas with the air or heat retention gas, and feeding this to the sintering material layer to produce sintered ore. This method premixes coke oven gas (COG) or LPG or other combustible gas with the air or heat retention gas and supplies the mix to the sintering material layer in that state so as to thereby use the heat generation by combustion of the gas in the sintering material layer to make up for the rise of the highest temperature of the temperature distribution curve at the stage of sintering of the upper layer part of the sintering material and the insufficient high temperature holding time and thus improve the yield and strength of the sintered ore. D3 discloses a method of providing a hood over the sintering material layer in the strand direction of the sintering machine, mixing a combustible gas and low melting point solvent with an oxygen-containing gas, and blowing this on the sintering material layer while producing the sintered ore. This method simultaneously blows a combustible gas and combustion assisting oxygen-containing gas to thereby increase the combustion rate of the combustible gas and coke breeze and further feeds a low melting point solvent adjusted in chemical composition or coke breeze or other carbon material to thereby increase the amount of liquid phase necessary for forming the sinter cake and thus improve the production rate of the sintered ore. Further, the method shown in D4, in the same way as D2, discloses the art of providing a gaseous fuel feed system and hood over the sintering material layer in the strand direction of the sintering machine, feeding blast furnace gas (BFG), coke oven gas (COG), LPG, or other gaseous fuel, and controlling the temperature distribution curve. This method controls the feed rate of the gaseous fuel so as to keep low the highest temperature of the curve of temperature distribution in the sintering material layer while adjusting the high temperature holding time to become longer. It improves the safety as related to the handling of a gaseous fuel while improving the production rate and yield of the sintered ore. However, these arts of use of auxiliary heat sources predicated on the supply of a combustible gas and methods of control of the temperature distribution curve have the three problems explained next. The first problem is the danger of backfire or explosion unique to mixing combustible gas. All of D2 to D4 are predicated on use of the combustible gas at less than the lower explosive limit concentration, so the rate of feed of the gas is restricted. If delays in control of the combustible gas concentration, abnormalities in the meters, etc. result in the lower explosive limit concentration being exceeded, fire will propagate from the sintering material layer to the above hood or gaseous fuel feeder and may lead to a large-scale explosion or fire. D3 discloses the art of adjusting the concentration of gas to prevent explosion. However, even if this safe method of feed is adopted, in a sintering method feeding a combustible gas as auxiliary fuel, supply of an amount of combustible gas over the lower explosive limit concentration is difficult. In principle, there are therefore limits to the amount of heat supplied to the sintering material layer. The second problem is the incomplete nature of the gas seal between the hood for feeding combustible gas and the top surfaces of the sintering pallets. Blast furnace gas (BFG), coke oven gas (COG), etc. contains carbon monoxide and other harmful components, so careful handling is required. The sintering pallets and surface of the sintering material layer are constantly in motion in the sintering machine strand direction, so completely sealing the interface between the fixed position combustible gas feed hood and the top surface of the moving sintering pallets is difficult. Therefore, when the negative pressure of a suction blower falls and when a sporadic accident causes the suction blower to stop, there is the unavoidable possibility of these harmful gases or combustible gas blowing out to the surroundings from the clearance between the hood and sintering material layer surface or clearance between the hood and the sintering machine pallets. In general, a sintering machine is installed inside a building, so when these gas leak out, there are concerns not only regarding the safety of the workers, but also the danger of fire due to the combustible gas building up inside the safety structure. The third problem is that to feed combustible gas to the sintering material layer, installation of a bulky hood above the sintering material layer in the strand direction of the sintering machine is unavoidable. In scheduled repairs of the sintering machine, the used sintering pallets are hoisted up by a ceiling crane and conveyed outside of the sintering machine several units at a time, while refurbished sintering pallets are loaded by the reverse procedure. Such exchange work is routinely carried out. When installing a combustible gas feed hood or feeding device above the sintering material layer in the strand direction of the sintering machine, these present obstacles to the sintering pallet exchange work and greatly prolong the repair time and causes other problems. DISCLOSURE OF INVENTION The present invention was made in consideration of the above situation and has as its object the provision of a method for the production of sintered ore as a material to be charged into a blast furnace in the process of production of pig iron in which use of an auxiliary heat source not dependent on conventional coke breeze, heavy oil, or gaseous fuel is made possible and the product yield and strength of the sintered ore in the sintering process are fundamentally improved and a sintering machine for the same. Furthermore, the present invention has as its object the provision of a novel sintering method enabling the reduction of the prime unit of amount of suction air per amount of production of sintered ore and reduction of the amount of consumption of electric power by the blower and further enabling the reduction of the exhaust load of controlled substances of air environment regulations due to the reduction in the amount of exhaust gas itself and the reduction in the NOx emission amount and a sintering machine for the same. The inventors engaged in research and development on measures for improving the yield of the upper layer part of a sintering material layer. In the process of this, as a measure for dealing with the insufficient heat of the upper layer part, they focused on the technical idea of utilizing high volatility liquid fuel and investigated the properties and studied the method of use of various liquid fuels. As a result, they confirmed the effectiveness of the method of sintering by directly spraying the surface of a sintering material layer with a high volatility liquid fuel. The present invention is configured as follows. (1) A method of production of sintered ore charging sintering pallets of a Dwight-Lloyd sintering machine with a sintering material comprised of an iron-bearing material, fluxes, and solid fuel and using an ignition furnace to ignite the solid fuel at a surface layer part of the sintering material, then sucking air from above downward in the sintering material layer to continuously promote a sintering reaction, the method of production of sintered ore characterized by spraying a liquid fuel spraying range set over an entire range of a sintering machine strand direction from where the sintering pallets leave an exit side of an ignition furnace to a sintering completion position, or any range thereof, from above the sintering material layer surface with a liquid fuel having a boiling point within the range of 60°C to 175°C. (2) A method of production of sintered ore as set forth in (1), characterized by adjusting an amount of spray of the liquid fuel in stages in the liquid fuel spraying range so that the further to a downstream side of the sintering machine strand direction from the ignition furnace exit side to the sintering completion position, the smaller the amount of spray of liquid fuel per unit area. (3) A method of production of sintered ore as set forth in (2), characterized by spraying at least 80% of a total amount of spray of the liquid fuel in the liquid fuel spraying range in a range from the ignition furnace exit side to a front 30% position of the machine length. (4) A method of production of sintered ore as set forth in any of (1) to (3), characterized supplying heat corresponding to 1% to less than 50% of the total heat input by the solid fuel and the liquid fuel by the liquid fuel. (5) A method of production of sintered ore as set forth in any of (1) to (4), characterized by controlling an amount of spray of the liquid fuel in the liquid fuel spraying range so that a measured value of concentration of oxygen in exhaust gas in a wind box or wind leg arranged below a sintering pallet is 2% or more. (6) A method of production of sintered ore as set forth in any of (1) to (5), characterized by controlling an amount of spray of the liquid fuel in the liquid fuel spraying range so that a measured value of concentration of NOx in exhaust gas of the sintering machine discharged through each wind box arranged below the sintering pallets is not more than a reference value. (7) A method of production of sintered ore as set forth in any of (1) to (6), characterized by spraying liquid fuel so that in a width direction of the sintering pallets, the amounts of spray of liquid fuel in ranges of 500 mm from the two side walls are greater than the other ranges. (8) A method of production of sintered ore as set forth in any of (1) to (7), characterized by using as the liquid fuel an organic compound with a vapor pressure at a 20°C ordinary temperature state of 0.1 kPa or more. (9) A method of production of sintered ore as set forth in (8), characterized in that the liquid fuel is an organic compound comprised of one or more types of compounds of chain like aliphatic hydrocarbons and alicyclic and aromatic hydrocarbons. (10) A method of production of sintered ore as set forth in (9), characterized in that the liquid fuel is an organic compound comprised of one or more types of compounds of alcohols having hydroxy groups or hydrocarbons containing oxygen atoms in their chemical structural formulas. (11) A sintering machine provided with a group of sintering pallets comprised of a plurality of sintering pallets endlessly connected with each other, a material feed system for feeding the sintering pallets with a sintering material, an ignition furnace for igniting solid fuel at a surface part of the sintering material, and a wind box arranged right below each sintering pallet for sucking air from above the sintering material layer downward, the sintering machine characterized by setting a liquid fuel feed system for spraying liquid fuel from above the sintering material layer to the sintering material layer surface in an entire range of the sintering machine strand direction from the ignition furnace exit side to a sintering completion position or any range of the same. (12) A sintering machine as set forth in (11) characterized in that the liquid fuel feed system is provided with a plurality of spray nozzles in a width direction of the sintering pallets. The specific constitution of the present invention will be explained below. In the general process of production of sintered ore, iron-bearing material comprised mainly of powdery iron ore and partially containing ironmaking refuse, returned ore, etc. is mixed with limestone, silica, serpentine, periodotite, and other fluxes and coke breeze, anthracite, and other solid fuel to form a sintering material. This is mixed and granulated to form granules, then the granulated material of the sintering material is fed to a sintering machine. In the sintering machine, a drum feeder or other charging device is used to charge the sintering material into a plurality of sintering pallets moving in the sintering machine strand direction and form a predetermined thickness of a sintering material layer. Next, an ignition furnace is used to ignite the solid fuel at the surface layer part of the sintering material layer, then wind boxes arranged below the sintering pallets are made to be negative pressure by using a main blower to suck air from above the sintering material so as to make the combustion of the solid fuel in the sintering material propagate successively downward. At this time, due to the heat generation by combustion of the solid fuel, the iron ore and fluxes in the sintering material partially melt and a liquid phase sintering reaction proceeds. As means for promoting or freely controlling this liquid phase sintering reaction, the combustion reaction of liquid fuel is utilized as a first feature of the present invention. In the present invention, the liquid fuel is sprayed over the surface of the sintering material layer over a liquid fuel spraying range set to the entire range of the sintering machine strand direction from the exit side of the ignition furnace to the sintering completion position or to any range of the same. As the method of spraying the liquid fuel, there is no need for making the liquid fuel a complete mist state. It is sufficient to structure the nozzles so that the liquid fuel substantially uniformly extends over the spraying range. That is, they may be nozzles such as shower nozzles or tips of spray cans forming large drops of liquid or nozzles such as agrochemical spray nozzles forming small drops of liquid. When the flow rate is small, continuous spray is not necessarily required. Even with intermittent spray at a cycle of several seconds to 20 seconds, the advantageous effects of the present invention can be enjoyed. However, with nozzles of a type forcibly mixing air with the liquid to atomize the same, backfire might be caused depending on the type of the liquid fuel or the atomization conditions, so care is required at the time of use. The actions caused by the liquid fuel sprayed over the sintering material layer in the above liquid fuel spraying range will be explained below. The liquid fuel sprayed over the sintering material layer once permeates the sintering material layer in the liquid state. After that, it robs the sintering material layer of sensible heat, vaporizes in exactly an amount commensurate with the equilibrium vapor pressure, is conveyed by air and moved downward in the sintering material layer, and reaches the vicinity of the combustion zone of the solid fuel. The combustion zone of the solid fuel in the sintering material layer is a high temperature region reaching near 1400°C, so the vaporized fuel reaches the ignition point in the high temperature region right before reaching the combustion zone, naturally burns and generates heat, and thereby raises the temperature inside the sintering material layer. This method of supply of liquid state fuel to the sintering material layer at room temperature has the following three features compared with the methods of supply of combustible gas shown in D2 to D4. The first feature is the ability to greatly reduce the risk of backfire and explosions. The general liquid fuel prescribed in the present invention has a high ignition temperature at ordinary temperature, so there is no concern over spontaneous ignition. When vaporizing and becoming a concentration exceeding the lower explosive limit, the danger of fire or explosion arises, but in the present invention, the liquid fuel vaporizes only within the sintering material layer. If burning only inside the sintering material layer, there is no danger in disaster management. Further, the treatment by spraying liquid fuel has a similar advantageous effect as spreading water. It robs the latent heat of evaporation at the time of vaporization, so has the action of lowering the temperature of the sintering material layer surface 5 to 10°C. This cooling effect as a result has the action of reducing the danger of ignition of the liquid fuel during spraying. The second feature is the smaller problem of leakage of harmful substances etc. in the workplace environment around the sintering machine. When using a combustible gas as fuel, there is the danger of the entire amount of the fuel supplied to the sintering material easily leaking and diffusing into the air, so the sealability between the supply hood and sintering machine is an important issue in safety management and disaster management. In the supply of liquid fuel in the present invention, the equilibrium vapor pressure of the liquid fuel at ordinary temperature is originally low, so there is a much smaller danger of reaching a concentration where toxicity would be a problem or an explosive concentration. Of course, liquid fuel also is a combustible substance having the danger of ignition and spread and is a substance having toxicity, but in general is widely being used as automotive fuel or household fuel. By management along with standards for handling of hazardous materials, reliable safety and disaster management is possible. The third feature is the greater compactness of the fuel feed system. The fuel feed system of liquid fuel can be made much smaller than the facilities for supplying combustible gas. When using a combustible gas as a fuel, it is necessary to prevent leakage and diffusion of the combustible gas to the surrounds, so it is necessary to install a fixed supply hood such as illustrated in Dl to D3 above the sintering material layer along the sintering machine strand direction. In the present invention, the fuel is sprayed in the liquid state over the sintering material layer surface, so it is sufficient to set just spray nozzles above the sintering material layer along the sintering machine strand direction. There is no need to set a hood or other fixed large-sized facility. The liquid fuel piping and spray nozzles also can be made of much smaller hardware compared with a combustible gas feed system since the fuel supplied is a liquid. At the time of scheduled repairs, they can be easily detached etc., so servicing is easy. Further, regarding the method of storage as well, with a combustible gas, a large gas holder is required, but with a liquid fuel, a small sized tank can be used. The specific spraying range and amount of spray of the liquid fuel for further enhancing the advantageous effect of the present invention will be explained below. First, a liquid fuel spraying range is set above the sintering material in the sintering machine strand direction from the ignition furnace exit side of the sintering machine to the sintering completion position, a plurality of pipes with spray nozzles (below, called "spray nozzle piping") are arranged in that range, and liquid fuel is fed from a liquid fuel storage tank through a liquid fuel feed pipe (header pipe) to the spray nozzle piping. The method of arranging in the strand direction of the sintering machine a plurality of spray nozzle piping extending in directions perpendicular to the strand direction (width directions) is simplest. These spray nozzle pipings are provided with wide-angle spray nozzles at for example 10 to 20 locations in accordance with the widths of the pallets of the sintering machine so as to enable even spraying over the entire width direction. Note that, the present invention is not limited to such a method of arrangement of spray nozzles or structure of spray nozzle piping. Any structure may be employed so long as the system can spray liquid fuel uniformly in the width directions. Furthermore, a plurality of such spray nozzle piping is arranged in this range of spraying of liquid fuel in parallel in the strand direction of the sintering machine. Regarding the pitch of installation of the spray nozzle piping, it is preferable to spray the liquid fuel extremely evenly over the sintering material layer surface, but it is not necessarily required to spray it without a break over the sintering machine strand direction. Even if areas are formed where liquid fuel is not sprayed between one piping and another piping, there is no problem in practice. The reason is that with the supply of usual liquid fuel, the feed rate of the liquid fuel is faster than the evaporation rate, so liquid fuel remains in the sintering material layer as a liquid. This buffer time, while depending on the type of the liquid fuel or the spraying conditions, is usually considered to be about 10 to 40 seconds, so the installation intervals of the piping may be made a pitch of 2 m or so without problems in use. For this piping interval, it is necessary to select the optimum conditions based on the above thinking while considering the type and feed rate of the liquid fuel and the speed of movement of the sintering machine pallets etc. Another feature of the present invention is that by using liquid fuel which is in a liquid state at room temperature, it is easy to adjust the flow rate for each spray nozzle arranged in the sintering machine strand direction. This technique will be explained below. In the prior art using a combustible gas, it is difficult to partially finely change the concentration of combustible gas or air ratio inside the supply hood. However, in the present invention using liquid fuel as auxiliary fuel, it is possible to freely adjust the amounts of spray of the liquid fuel in the strand direction of the sintering machine and the width directions of the sintering pallets in nozzle units. First, the method of adjustment of the amounts of spray of the liquid fuel in the width directions of sintering pallets will be explained. Regarding the distribution of yield of sintered ore at the different positions of the sinter cake in the width directions of the sintering pallets, for example, as shown in FIGS. 4(a) and (b) showing one example of measured results, there is a tendency for the yield to drop in the ranges of up to 500 mm from the side walls at the two sides of the sintering pallets in the width directions. This tendency is more remarkable in the large-sized sintering machine B. The reason is that the rise in temperature of the side walls themselves, the dissipation of heat from the side walls to the outer air, etc. tend to cause the parts of the sintering material layer near the side walls to be insufficiently heated. D4 discloses the art of feeding gaseous fuel as the means for making up for the insufficient firing near the side walls, but with this method, the problem of the incompleteness of the seal explained as the second problem relating to the technique of feeding a combustible gas remains. That is, achieving a complete seal between the fixed hood supplying the gaseous fuel and the moving body of the sintering material layer surface is technically difficult. The effect of gaseous fuel feed parts near the side walls and the air at the center of the pallets in the width direction being mixed above the sintering material layer or in the sintering material layer is reduced, so a sufficient effect is hard to obtain. Complicated adjustment of the feed rates so as to feed different concentrations of gaseous fuel in the width directions of the sintering pallets is also substantially difficult. In the present invention using a liquid fuel, the liquid fuel can be concentratedly fed to the parts of the sintering material layer surface near the side walls. Therefore, it is possible to selectively supply auxiliary heat to the regions with a low product yield in the ranges of up to 500 mm from the side walls at the two sides of the sintering pallets in the width direction so as to improve the product yield. Further, the degree of aging of the sintering pallets and their side wall differs with each sintering machine, so the ranges from the side walls where the product yield is lower will differ somewhat with each sintering machine, but it is possible to change the installation intervals of the nozzles of the liquid fuel in the width directions of the sintering pallets each time so as to easily finely adjust the spraying range and the amounts of spray. For example, it is possible to set the intervals between spray nozzles in the width directions at a small 100 mm pitch just in the ranges of 500 mm from the side walls to make the amounts of spray larger the closer the nozzles to the side walls and otherwise finely control the distribution of the amounts of spray in the width direction. Next, the method of adjustment of the amounts of spray of liquid fuel in the strand direction of the sintering machine will be explained. The inventors engaged in sintering tests using a number of types of organic compounds as liquid fuel liquid at room temperature so as to investigate the curves of temperature distribution in the sintering material layer and the changes in the concentrations of components in the exhaust gas. As typical examples, test results in the case of using ethanol (test 1) and n-octane (test 2) are shown in FIGS. 5(b) and (c). Note that, in FIGS. 5(b) and (c), T1 shows the temperature distribution curve in the case where the coke breeze combustion zone is positioned at a height of 450 mm (upper layer position), T2 shows the temperature distribution curve in the case where the coke breeze combustion zone is positioned at a height of 300 mm (middle layer position), and T3 shows the temperature distribution curve in the case where the coke breeze combustion zone is positioned at a height 110 mm (lower layer position). In this test, an inside diameter 300 mm x height 600 mm sintering test system, the mixed materials shown in Table 1 were charged and a sintering test conducted. In the 6 minutes from 3 minutes to 8 minutes after the start of ignition of the sintering material layer surface, a spraying test was run spraying each of the various types of liquid fuel shown in Table 3 in an amount of 7 kg per ton of mixed materials. The sintered ore was measured for changes in production rate, product yield, quality, and exhaust gas oxygen concentration. A summary of the test results is given in Table 4. Note that, regarding the heavy oil spraying test shown in Comparative Example 5, under the test conditions of starting spraying 3 minutes after the start of ignition, the heavy oil remained unburned, so the test conditions were changed so as to spray it in the 1.5 minutes from 1.5 to 3.0 minutes after the start of the drop. Table 3. List of Properties of Liquid Fuel Used in First Examples and Comparative Examples Table Removed : ETBE: ethyl tertiary butyl ether Table 4. List of Sintering Test Results in First Examples and Comparative Examples Table Removed . FFS:flame front speed (rate of descent of front of sintering combustion) (mm/min) *3. SI: remaining rate of 10 mm or larger grains after 10 mm or larger grains of sintered ore are dropped 4 times from 2 m height (mass%) *4. NOx: concentration of nitrogen oxides converted to oxygen concentration 15% (ppm) From the results of Table 4, at all of the test levels shown in Examples 1 to 9, compared with Comparative Example 1 where no liquid fuel was sprayed, an effect of improvement of the product yield and production rate of the sintered ore was observed. Further, under the conditions of all of Examples 1 to 9, a trend toward coarsening of the granularity of the sintered ore was seen. The cold strength of the sintered ore was also greatly improved. Furthermore, the concentration of oxygen in the exhaust gas exhausted in the sintering process fell and a reduction in the NOx exhaust concentration was confirmed as well. From the above tests, due to the supply of liquid fuel, an improvement in the rate of utilization of oxygen in the sintering reaction, a rise in the coke breeze combustion temperature, and furthermore a large effect of improvement of the production rate and quality of the sintered ore as results of operation could be confirmed. On the other hand, regarding Comparative Example 2 using phenol as a liquid fuel, part of the high melting point phenol solidified inside the sintering material layer, so the air permeability of the sintering material layer dropped and the FFS (flame front speed) and sintered ore production rate deteriorated compared with even Comparative Example 1. Regarding Comparative Example 3 using acetone as the liquid fuel, the effect of improvement of the product yield and strength of the sintered ore was relatively small compared with the liquid fuels of Examples 1 to 9. A trend of the FFS rather dropping was seen. The resultant effect of improvement of the production rate of the sintered ore was also limited. This is believed due to the fact that acetone has a low boiling point and high vapor pressure, so the sprayed acetone burns in the space above the sintering material layer and therefore the inherent effect of raising the temperature of the high temperature part in the distribution of temperature in the sintering material layer was not sufficiently obtained. Regarding Comparative Example 4 using ethylene glycol as the liquid fuel, no clear difference from Comparative Example 1 could be confirmed. Ethylene glycol has a low vapor pressure, so cannot sufficiently vaporize in the sintering material layer and is believed to be discharged to the cooler while remaining inside the sinter cake. Regarding Comparative Example 5 in which heavy oil is used as the liquid fuel, fire and smoke were seen at the sintered ore surface right after spraying, but the production rate and sintered ore quality were improved. However, regarding the concentration of SOx in the exhaust gas, it was confirmed to be much worse than either Comparative Example 1 or Examples 1 to 9. Second Examples A sintering area 600 m2, pallet width 5 m, machine length 120 m sintering machine was provided with liquid fuel spray nozzles such as shown in FIG. 2. Operational tests were run changing the amount of spray of the liquid fuel and spray positions. The mix of materials used in this test is shown in Table 5. During this test, it was assumed the mix of materials did not change. The operational tests were run under stable conditions fixing the layer thickness of the sintering machine at 580 mm and the negative pressure at 1600 mmAq. The test levels of the spraying of liquid fuel are shown in Table 6. Ethanol was sprayed as a liquid fuel in an amount corresponding to 3.5 kg or 7.0 kg per ton of mixed materials and comparative tests run against operations not spraying liquid fuel. The spraying positions were divided into an A zone (machine length 5 to 30% range), a B zone (machine length 30 to 50% range), and a C zone (machine length 50 to 80% range). Operational tests were run adjusted to the plurality of patterns shown in Table 6. Table 5. Mixing Conditions of Materials in Actual Test Table Removed Table 6. Test Conditions Relating to Second Examples and Comparative Examples Table Removed *5. Agglomerating material ratio: total amount of solid carbon sources (coke breeze and anthracite) per ton of mixed materials (kg/t-mixed materials) *6. Liquid fuel mixing ratio: amount of use of liquid fuel per ton of mixed materials (kg/t-mixed materials) *7. Liquid fuel heat ratio: heat ratio of liquid fuel in total input heat of solid agglomerating materials and gaseous fuel and liquid fuel (-) The test results are shown in Table 7. Compared with Comparative Example 5 in which no ethanol was sprayed, Examples 10 to 14 all exhibited effects of improvement of the sintered ore production rate, product yield, strength, and granularity distribution. For Example 15, the FFS was poor, so no change was seen in the production rate, but effects of improvement of the sintered ore product yield, strength, and granularity distribution were confirmed. Table 7. List of Results of Sintering Test in Second Examples and Comparative Examples Table Removed *8. TI: rotating strength JIS (rotating strength test) By comparison of Comparative Example 5, Example 10, and Example 11 changed in amounts of spray of ethanol, it was confirmed that the more the amount of spray of ethanol is increased, the greater all of the effects of improvement. In the results of comparison of Example 11 to Example 15 changed in pattern of spraying ethanol, it was confirmed that there was an effect of improvement of the production rate, strength, etc. of the sintered ore under the conditions of the level of Examples 11 to 13, that is, a spray ratio in the A zone of 60% or more. In Example 14 given a spray ratio in the A zone of 40%, the effect of improvement of the production rate and strength of the sintered ore was somewhat smaller, but in terms of the reduction of the concentration of oxygen in the exhaust gas and of the NOx, a greater improvement was exhibited compared with Comparative Example 5 or even Example 12 giving the greatest production rate. Regarding Example 15 where the spraying ratio of the A zone was made 20% and the spraying ratios in the B zone and C zone were made 4 0%, the product yield and strength of the sintered ore were improved, but the FFS greatly deteriorated, so the production rate was not improved over Comparative Example 5. However, for the concentration of exhaust gas, an effect of reduction of the NOx substantially equal to that of Example 13 or 14 could be confirmed. Third Examples Using the same sintering machine, material mix, operating conditions, and liquid fuel spray conditions as in Example 11 of Table 7, a test was run adjusting the amounts of spray of the liquid fuel spray nozzles in the width direction. In this test, 50% more liquid fuel than at the center part was sprayed at the parts in the ranges of 500 mm from the side walls at the two sides of the sintering pallets. However, the total amount of liquid fuel sprayed was matched with the 7.0 kg per ton of mixed materials the same as the example. The results of the survey of the yield distribution of the sinter cake obtained in this test are shown in FIG. 7. Under conditions of uniform spraying of ethanol in the width direction (FIG. 7(a)), a drop in yield near the side walls was seen, but under conditions of increasing the amounts of spray near the side walls (FIG. 7(b)), sinter cake having a high yield up to the clearances with the side walls was produced. As a result, the product yield of sintered ore in a sintering operation was improved 2.0% compared with Example 11. An effect of improvement of 0.8t/d/m2 for production rate was also confirmed. INDUSTRIAL APPLICABILITY As explained above, according to the method of production of sintered ore and sintering machine of the present invention, it is possible to improve the product yield and strength of sintered ore. Further, compared with the case of the conventionally used gaseous fuel or other auxiliary heat source, it is possible to avoid the danger of backfire and explosions and reduce the amount of exhaust gas and reduce the amount of NOx emission and thereby keep down the production of air environment controlled substances. Furthermore, practical excellent effects such as the improvement of maintenance work of the sintering facilities due to the greater compactness of the auxiliary heat supply facilities can be expected. The industrial applicability can be said to be extremely great. CLAIMS 1. A method of production of sintered ore charging sintering pallets of a Dwight-Lloyd sintering machine with a sintering material comprised of an iron-bearing material, fluxes, and solid fuel and using an ignition furnace to ignite the solid fuel at a surface layer part of said sintering material, then sucking air from above downward in the sintering material layer to continuously promote a sintering reaction, said method of production of sintered ore characterized by spraying a liquid fuel spraying range set over an entire range of a sintering machine strand direction from where said sintering pallets leave an exit side of an ignition furnace to a sintering completion position, or any range thereof, from above the sintering material layer surface with a liquid fuel having a boiling point within the range of 60°C to 175°C. 2. A method of production of sintered ore as set forth in claim 1, characterized by adjusting an amount of spray of the liquid fuel in stages in said liquid fuel spraying range so that the further to a downstream side of the sintering machine strand direction from the ignition furnace exit side to the sintering completion position, the smaller the amount of spray of liquid fuel per unit area. 3. A method of production of sintered ore as set forth in claim 2, characterized by spraying at least 80% of a total amount of spray of the liquid fuel in said liquid fuel spraying range in a range from the ignition furnace exit side to a front 30% position of the machine length. 4. A method of production of sintered ore as set forth in any of claims 1 to 3, characterized supplying heat corresponding to 1% to less than 50% of the total heat input by said solid fuel and said liquid fuel by the liquid fuel. 5. A method of production of sintered ore as set forth in any of claims 1 to 4, characterized by controlling an amount of spray of the liquid fuel in said liquid fuel spraying range so that a measured value of concentration of oxygen in exhaust gas in a wind box or wind leg arranged below said sintering pallets is 2% or more. 6. A method of production of sintered ore as set forth in any of claims 1 to 5, characterized by controlling an amount of spray of the liquid fuel in said liquid fuel spraying range so that a measured value of concentration of NOx in exhaust gas of the sintering machine discharged through each wind box arranged below said sintering pallets is not more than a reference value. 7. A method of production of sintered ore as set forth in any of claims 1 to 6, characterized by spraying liquid fuel so that in a width direction of said sintering pallets, the amounts of spray of liquid fuel in ranges of 500 mm from the two side walls are greater than the other ranges. 8. A method of production of sintered ore as set forth in any of claims 1 to 7, characterized by using as said liquid fuel an organic compound with a vapor pressure at a 20°C ordinary temperature state of 0.1 kPa or more. 9. A method of production of sintered ore as set forth in claim 8, characterized in that said liquid fuel is an organic compound comprised of one or more types of compounds of chain-like aliphatic hydrocarbons and alicyclic and aromatic hydrocarbons. 10. A method of production of sintered ore as set forth in claim 9, characterized in that said liquid fuel is an organic compound comprised of one or more types of compounds of alcohols having hydroxy groups or hydrocarbons containing oxygen atoms in their chemical structural formulas. 11. (Amended) A sintering machine provided with a group of sintering pallets comprised of a plurality of sintering pallets endlessly connected with each other, a' material feed system for feeding the sintering pallets with a sintering material, an ignition furnace for igniting solid fuel at a surface part of the sintering material, and a wind box arranged right below each sintering pallet for sucking air from above the sintering material layer downward, said sintering machine characterized by setting a liquid fuel feed system for spraying liquid fuel having a boiling point within the range of 60°C to 175°C from above said sintering material layer to said sintering material layer surface in an entire range of the sintering machine strand direction from said ignition furnace exit side to a sintering completion position or any range of the same. 12. A sintering machine as set forth in claim 11 characterized in that said liquid fuel feed system is provided with a plurality of spray nozzles in a width direction of said sintering pallets.