Introduction to the Results: The use of mixed diesel fuel is one of the effective solutions to achieve energy saving and emission reduction in diesel vehicles. This project conducted systematic research on key technologies for hybrid diesel fuel vehicles from three aspects: 'Composition and Physical and Chemical Properties, Engine Matching Technology, and Vehicle Application Demonstration', breaking through the application bottleneck of diesel alternative fuels and promoting the application and development of hybrid diesel fuel technology. The main achievements include: establishing a system of guarantee methods for the composition and physical and chemical properties of mixed diesel fuel; inventing low-cost, high-efficiency biodiesel antioxidants and low-temperature flowability improvement methods, a new generation of low-cost, high-performance emulsifiers, and a high-stability emulsion diesel production process, solving problems such as poor oxidation stability and low-temperature flowability of biodiesel, and storage stability of mixed diesel fuel. Overcoming the key technology of matching mixed diesel fuel with engines. Establishing a database of material compatibility for mixed fuel engines. An empirical spray formula suitable for mixed diesel fuel was proposed, which does not alter the engine structure and provides the optimal mixing ratio; a low NOx, low particulate matter emission aftertreatment technology for mixed diesel fuel engines was invented, solving the key technical problem of matching mixed diesel fuel with engines. A systematic demonstration project involving the application of mixed diesel fuel in 70 diesel taxis, 132 diesel buses, and 140 diesel freight vehicles was carried out, with a cumulative demonstration mileage of 43.64 million kilometers. Specifications for the whole vehicle application demonstration of mixed diesel fuel were established, addressing issues exposed during the application demonstration and promoting the application and development of mixed diesel fuel technology. The project has authorized 4 invention patents, applied for 7 invention patents, granted 3 utility model patents, and published 77 papers (including 6 SCI-indexed and 30 EI-indexed). The project achievements have led to the application and development of mixed diesel fuel technology. It has achieved energy saving and emission reduction for diesel commercial vehicles and passenger cars, protected the urban atmospheric environment, and promoted significant progress in the production and application technology of diesel alternative fuels. It is not only suitable for mixed diesel fuels such as biodiesel, synthetic fuel, and emulsified diesel but can also be promoted to other areas of diesel alternative fuels and mixed gasoline fuels.