A theoretical study of a ®nite grooved journal bearing lubricated with couple stress¯uids is made considering both thermal and cavitation effects. On the basis of the Stokes couple stress¯uid model, the modi®ed Reynolds equation and the energy equation are derived and then numerically solved together with the heat conduction equation. The solution to the modi®ed R eynolds equation is determined using the Elrod cavitation algorithm. The effects of couple stress on the performance of a journal bearing are investigated. It is observed that the lubricants with couple stress, compared with N ewtonian lubricants, not only yield an obvious increase in load capacity and decrease in coef®cient of frictio n but also produce a slight increase in the temperature of lubricants and bush and a slight decrease in the side leakage¯ow.
Multiple-injection technology is being widely used in common-rail injection (CRI) systems for diesel engines. The precise control of the injected fuel quantity (FQ) and timing of every injection will directly affect the engine efficiency and exhaust performance. As the engine speed becomes faster, when more than five injections are engaged in per combustion cycle, the injection interval (between consecutive injections) will become increasingly shorter. In experiments based on the green diesel (GD)-CRI system applied in the YC6112 engine, the FQ of the main injection (MI) was found unbalanced when the pilot injection (PiI) is very close to it. According to the experimental analysis, this phenomenon was validated to mainly result from the electrohydraulic delay and the fuel pressure waves in the line leading from the rail to the injector. In order to minimize this influence, a software compensating strategy, which made an additive correction of the injection quantity, was developed. By this optimized software, not only does the MI FQ become steadily even when the PiI is very close to it, but also the conventional system-restricted injection interval can be decreased to as short as possible. This contributes to fulfilling the multiple-injection technology in the GD-CRI system and provides further benefit for the triple-injection function or greater. It also provides a successful example for up-to-date CRI systems to improve the multiple-injection performance in any other engine types by this software optimization method.
Besides the common-rail system, the electronic unit pump (EUP) is also being widely used in electronically controlled diesel engines. However, the EUP system is restricted for use in EURO IV diesel engine development, as its consistency of fuel delivery is hard to control accurately. As has been found in the case of the Chinese home-made EUP system, this problem is mainly caused by mechanical manufacture. In spite of the low-class hardware limit, this paper introduces a software method to correct the inconsistency of fuel delivery among EUPs at the whole range for engine running. First, the characteristics of inconsistency of fuel delivery among EUPs are determined based on a series of experiments. Second, an optimization algorithm with multi-point correction is proposed to adapt to the tendency for non-linear inconsistency. Finally, the algorithm is verified on the fuel pump testing platform, made by EFS company, and further on a YC6J diesel engine. The experiments demonstrate that the multi-point correction is not only able to weaken the inconsistency of fuel delivery among EUPs, but also improves both the idling control and the emission performance for an electronically controlled diesel engine. This paper also provides a successful example of an electronically controlled diesel engine where the consistency of fuel delivery from cylinder to cylinder is improved by this software optimization method.
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