The piston ring pack is one of the most important components to affect the power, economy and emission of a diesel engine. Among them, lube oil consumption (LOC) and crankcase blow-by (CB) are the main indicators to evaluate the lubrication and sealing performance of the piston ring pack. In this study, the multi-factor analysis was implemented to predict the influencing factors on the LOC, CB and the sensitivity between them in the piston ring pack for an agricultural diesel engine. A YNF40 diesel engine was taken as the research object. Firstly, the test bench of LOC and CB was built for the diesel engine. The kinematics and dynamics models were established using hydrodynamic lubrication and gas flow theoretical of piston pack friction subsets, technical and structural parameters. A series of experimental tests were also carried out to verify the accuracy and reliability of the simulation. Secondly, the grey relational grade (GRG) of different influencing factors was obtained by grey relation analysis (GRA). The sensitivity analysis between the influencing factors and LOC-CB was then carried out using GRG calculation and ranking. Finally, the time-series prediction models were established for the transient variations of LOC and CB under different speed conditions using a back propagation (BP) neural network. The multi-factor GRG analysis indicated that the most sensitive influencing factor on the LOC and CB in the piston ring pack for a diesel engine was the chamfer of the bottom edge of the 1st ring groove of the piston, whereas, the most insensitive influencing factor was the back clearance of the 3rd ring groove of piston. The maximum GRG between LOC and CB and the chamfer of the bottom edge of the 1st ring groove of the piston was 0.89279, whereas, the minimum GRG between LOC and CB and the back clearance of the 3rd ring groove of the piston was 0.58361. The descending order of sensitivity was obtained between the target and influencing factors. The LOC and CB gradually increased in the piston ring pack for a diesel engine, as the chamfer of the bottom edge of the 1st ring groove of the piston increased. The back clearance of the 3rd ring groove of the piston shared no significant effect. The average standard deviation of the variation of LOC and CB with the chamfer of the bottom edge of the 1st ring groove of the piston were 2.81, and 3.90, respectively. By contrast, the average standard deviation of the variation of LOC and CB with the back clearance of the 3rd ring groove of the piston were 0.003 and 0.209, respectively. Therefore, the larger the GRG between LOC and CB, and each influencing factor were, the larger the mean standard deviation of LOC and CB with the influencing factors were, and the more sensitive the objectives were to the influencing factors. The time-series prediction showed that there was a better consistent trend of the predicted and actual values on the transient variations of LOC and CB. The prediction accuracy and reliability of the time series prediction model were higher than before, which were distributed within the 95% confidence band. The research findings can provide effective guidance to improve the thermal efficiency with the less carbon emissions of agricultural diesel engines.

Cold-start performance has been one of the most restricting factors in the internal combustion power equipment at in extreme cold conditions in plateau areas. The aim of this study was to explore the cold-start characteristics of diesel engines at different ambient temperatures in a plateau. Different strategies of fuel injection were then evaluated for the environmental adaptation. The research object was taken as the diesel engine with direct injection, high-pressure, and common rail. A test chamber with a low-temperature environment and a cold-start test bench were constructed on at the an altitude of 2 000 m. Then, the environmental adaptation experiments were carried out using 3 injection strategies at extreme cold conditions (the lowest ambient temperature was -45 ℃) in the plateau. The cold-start performances of diesel engines were evaluated with the different advanced angles of fuel injection. The results showed that the double injection (DI) and triple injection (TI) strategies were effectively improved the speed stability and reliability of the diesel engine cold-start in extreme conditions, compared with the single injection (SI) strategy. Furthermore, the strategies of fuel injection were ranked in the ascending order of TI < DI < SI, according to the delay timing of the combustion mean ignition. While the mean maximum combustion pressure was ranked in the opposite direction. Specifically, the longest delay of combustion ignition was observed in the SI strategy under cold-start conditions without the assistance of a glow plug, where the ignition delay was 4.5 ℃A after the top dead center. The ignition delay of the TI strategy was advanced by 5.6 ℃A, compared with the SI strategy, indicating the enhanced proportion of pre-mixed combustion. And tThen the uniform, stable, and high performance was achieved in the cold-start combustion of the diesel engine with the TI strategy. The optimal advance angle of fuel injection appropriately increased for the combustion of cold-start, which was 30 °CA BTDC. The largest peak of HC emission was generated by the diesel combustion using the SI strategy, while the middle and smallest peaks were found using the DI and TI strategy, respectively. Among them, the peak of HC emissions that generated by diesel combustion with the TI strategy decreased by 58.6% and 64.8% at 20 and -5 °C, respectively, compared with the SI strategy. The engine was started unsuccessfully at the temperatures of -25 °C and below for the SI strategy and -45 °C for the DI strategy. By contrast, the TI strategy was enabled on the engine cold-start performance in at one time in a wide temperature range of -45~20 °C. Particularly, the cold-start success rate was significantly improved for the average acceleration, in order to shorten the cold-start duration. Therefore, the diesel engine cold-start time of the SI strategy was the longest, the DI strategy was in the middle, and the TI strategy was the shortest under the cold-start conditions of consistent temperature. TI strategy was greatly improved the cold-start performance and environmental adaptation of the diesel engine under extreme cold conditions in the plateau. The research findings can also provide a strong reference to improve the cold-start performance and environmental adaptation of internal combustion power equipment under the a wide range of ambient temperatures in multiple regions.