Experimental Study And Method Of Reducing Fuel Consumption For Single Overhead Camshaft Gasoline Engine

Nowadays with the development of automobile industry, the problem we confronted with is not just of environment but also the scarcity of petroleum resource. More importance being put in to the issue of energy and environment, rules for the limitation of automobile emission gas and wastage of automobile has been or will be carried out by governments of many countries. Under this pressure the automobile industry is gradually paying much more attention to the development of technology for reducing the engine wastage and CO2, for advancing the capacity of fuel adequately burning. In this context, China has also carrying out the second-step standard for the limitation of automobile fuel consumption.Because the original 4G6 gasoline engine applies single overhead camshaft and natural to breath way, the valve lift could be unchanged. Therefore is hard to reach ideal distribution phase and the best of charge efficiency, fuel economy and power increase also for nothing tolerate easily further. By redesigning the 4G6 gasoline engine in increasing the compressing ratio, reducing the friction and perfectly timing the valve, we successfully adjust the 4G6 gasoline engine to the new standard. For this improvement objective, we mainly carried out the following experimental research:1) To make smaller of the concave volume of piston head, increasing the compressing ratio for 4G6 SOHC gasoline engine from 9.5 to 10. According to the definition of the ideal cycle's thermal efficiency of gasoline engine, along with the increase of compression ratio, this may increase mixture gas highest temperature, enlarged circulating temperature gradient, increased the expansion ratio and consequently increased the thermal efficiency, and then improve fuel consumption rate of gasoline engine;2) Increasing the top rings' surface pressure and the ring's tangential force so as to ensure that seal up high-strength compressed gas and combustion gas;3) Lower the piston ring's width to reduce the tangential force of the piston rings and friction loss; realizing the lightening of the engine and improving the fuel consumption.4) The cross section of piston ring and its major construction parameters are obtained to make sure of its use.5) Distribution mechanism is changed to Mitsubishi's MIVEC variable valve timing electronic control mechanism. In low-medium speed, different valve lift is used to strengthen the air-fuel mixture of the swirling, increase the mixture uniformity. The small valve overlap can decrease internal rate of EGR and improve low-speed combustion stableness, thereby improving fuel consumption, and reducing emissions. At the same time, the low valve lift can reduce friction loss and the scavenging volume, the charge efficiency is increased which in turn raised the low-speed torque. In the high-speed, high valve lift and scavenging impulse to improve the charge efficiency to enhance power is realized.6) Carrying out performance testing evaluation on the engine test bench and also the fuel consumption testing evaluation on automobile to verify the designing project. The results show that increasing the compression ratio and the use of low-tension piston ring of low consumption, performance and fuel consumption reach the initial target set by the development. The use of variable valve timing MIVEC body design, the engine's low-speed torque and high-speed performance have improved significantly. The minimum fuel consumption rate had achieved the development goals value of 250g/kWh on the test bench, and significantly wider economy zone is also reached. Finally two different models of vehicle that are carried horizontal engine or vertical engine arrangement were carried on the test of fuel consumption, test results showed that the vehicle with the improved design of engine can meet our country by using vehicle fuel consumption standards for the second phase of the threshold requirement.The summary of the research for this thesis is as follows:1) The increase of compressing ratio effects the fuel consumption of the engine clearly. In theory, the higher the compression ratio, the greater the efficiency of the engine. The reason for this is that combustion takes place faster because the fuel molecules are more tightly packed, the flame of combustion travels more shortly and the combustion speed is more rapidly. As a result, more complete combustion and lower fuel consumption rate are obtained. But when the compression ratio is higher to a certain extent, the thermal efficiency of the cycle will not significantly impact, and raising the compression ratio is also limited by the conditions of the structure, machinery and efficiency of the detonation, and other conditions, so different engine type to choose the right compression ratio.2) As the compression ratio increases, so that the temperature of combustion chamber will go up, which will make the NOx emissions are increasing. As a result, with compression ratio increases which need emission for post-processing. 3) The piston ring's tangential force has a big influence on the engine fuel consumption, the lower the force, the smaller the friction loss of the piston and piston ring, the higher the mechanism efficiency and the better fuel consumption, but the lower tangential force necessarily bring on the results that will inevitably lead to deterioration of scraping oil capacity, thereby it has adversely affected to the oil consumption;4) The piston rings'tangential force lies on the piston ring's surface pressure and the ring's width, even the surface pressure maintain unchanged, lower the ring's width can also achieve the tangential force lower;5) The top ring's outward pressure plays a vital role to the gas sealing. The greater pressure, the better the effect of sealing;6) The technology of MIVEC variable valve timing electronic control to improve the low speed in the region helps fuel economy. As the engine in the field of low speed zone to adopt a different valve lift, to strengthen the flow of the mixture to improve the combustion quality, improved cycle thermal efficiency and reduced friction loss, therefore, the direct benefits is the improved fuel economy and emission;7) The technology of MIVEC variable valve timing electronic control to improve engine power within high-speed field. As the domain of high-speed, high-valve lifts so that the charge efficiency, power has improved significantly.8) The engine management system is optimized calibration again, which can correspond to different engine operating conditions, as far as possible in order to make the best valve timing, to maximize charge efficiency, the best fuel consumption rate and emissions.