| The off-road diesel engines are mainly power, which are widely uesed as agricultural machines, engineering machines, forestry machines, marine ships, generators and pumps in our country. Because of the low price and the limit of cooling method and structures, the technologic development of horizontal off-road diesel engine lagged seriously in our country. The chief characteristics were the large volume, the heavy mass density, the low power per liter and the reliability, the short life, the bad cooling effect and fuel economy, and the serious noise and emission pollutant. Aiming at the technical matters of the existing horizontal off-road diesel engine, the key technical proposals for designing the high efficiency and low pollute off-road diesel engines were put forward, and the researching work were investigated as follows.(1) Researching the influent relationship of the structure of helical intake port to flow characteristics of the intake portAiming at the complex free curved surface characteristic of helical intake port, a top-down design way of helical intake port for diesel engine was put forward and the complicated three-dimensional model and the numerical simulation model of helical intake port for diesel engine were set up by establishing three-dimensional curve mathematical model of the helical section surface space and using curve association characteristic. The simulation model of intake port was built based on the steady flow experiments. The effects of the geometry parameters of helical intake port straight section and helical section and the intake valve position on the intake port and the gas flow characteristic in cylinder were researched and the key geometry parameters and the sensitive part of the intake port were analyzed.(2) Researching the structure of cooling jacket and flow characteristics of the cooling systemIn order to fulfill the technical requirements of a high-efficiency low-emissions off-road horizontal diesel engine, a unique design is proposed for the cooling water jacket structure with a forced-cooling closed-loop cooling system. The cooling water flow rate, temperature, and pressure at the inlet and several other critical locations of the cooling water jacket were measured and analyzed at different engine operating conditions for the water jacket design. A numerical simulation model of the coolant flow and the cooling system was built and used to analyze the thermal/fluid characteristics of the coolant flow in the water jacket. The impact of different structural and packaging design parameters on the coolant flow and heat transfer was investigated. The cooling water jacket structure and the water pump flow rate were optimized.(3) Researching the dynamics characteristics and influent factors of piston assemblyBased on the dynamics characteristics of piston assembly, the temperature distribution of the piston and cylinder liner was researched on the thermal load condition and the dynamic model of piston assembly was established. The influent relation of piston and piston rings structural parameters to the secondary motion of the piston assembly, the influent relation of oil consumption and gas leak to dynamics characteristic of piston assembly were researched based on the orthogonal design method.(4) Designing the high efficiency and low pollute horizontal off-road diesel engineA new type of high efficiency low pollute horizontal off-road diesel engine was designed based on the design and optimization of matching test of the combustion system, the innovative design and analysis of engine body, cooling system, lubrication system, piston assembly, valve trains and overall layout of other components. The structural characteristics and performance indices of this new engine are as follows:(1) The diesel engine was compact and light. The total mass was 221kg, and the specific mass was 6.05kg/kW with the state of naturally aspirated. The total mass was 227kg, and the specific mass was 4.54kg/kW after being strengthened by the exhaust turbocharger.(2) The fuel consumption was economical. At the full load characteristic working state of naturally aspirated, the lowest fuel consumption was 224g/(kW·h) and the effective fuel consumption was 234g/(kW·h) at the point of rated power. At the working state of turbocharged and intercooled, the lowest fuel consumption was 221g/(kW·h) and the effective fuel consumption was 246g/(kW-h) at the point of rated power. This showed that the effective fuel consumption area and the power adaptive range were wide to this diesel engine.(3) The lubricating oil consumption was lower. At the full load characteristic working state of naturally aspirated, the average oil consumption was 0.299 g/(kW·h) and the average fuel consumption ratio was 0.127%. At the working state of turbocharged and intercooled, the average oil consumption was 0.293 g/(kW·h) and the average fuel consumption ratio was 0.119%.(4) The exhaust emissions were low and worked reliably. The emissions were in accordance with the National stageⅡemission limits at the full load characteristic working state of naturally aspirated. And the reliability experiment of 1000 hours met the National Standard at the extra characteristics working state of naturally aspirated.
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