Investigation of the combustion deterioration of an automotive diesel engine under transient operation

With increasingly stringent emission regulations and demand for fuel economy by the public,the combustion and emission problems of automotive diesel engines during transient operation have become vital and urgent issues.In this study,combustion deterioration has been experimentally analyzed using a heavy-duty turbocharged diesel engine running under transient conditions(constant speed and increasing torque).Optimization of the transient combustion process was performed by adjusting the fuel injection parameters.The results indicated that the notable combustion deterioration relative to steady state operation while transient was a function of the delay in the air-supply to the turbocharged engine,and took the form of combustion phasing delay,resulting in rapidly increasing smoke emission and fuel consumption.However,the delay in combustion phasing can be controlled by advancing the fuel injection timing,effectively increasing thermal efficiency.Unfortunately,smoke and NO x emissions increased at the same time.The deterioration in combustion phasing can also be improved by increasing injection pressure,resulting in decreased smoke emission while NO x emission increased.It is worth noting that the effective thermal efficiency first increased and then decreased as fuel injection pressure increased during transient operation.

Long-term follow-up study of 72 patients with transient ischemic attacks

Objective To observe the long-term follow-up of 72 patients with transient ischemic attack (TIA) and evaluate the clinical significance of neurovascular surgical indication. Methods Seventy-two patients with TIA collected from years 1959 to 1977 were followed up by means of face-to-face communication with the patients themselves or their families till year 1998. According to the principle of life table, the recurrence of TIA after the first attack, occurrence of complete stroke and myocardial infarction, fatality rate, causes of death and survival rate every year, and the 95% confidence interval were calculated and analyzed.Results Till 1998, the recurrent rate of TIA in 72 patients was 27.9%, the occurrence rate of complete stroke 65.7%, and that of myocardial infarction 8.4%. The fatality rate was 72.7%. Among the deaths, 2 (3.8%) patients died of myocardial infarction. It was shown from the study that the main cause of death was complete stroke, accounting for 59.6% of all deaths, with the main cause in non-elderly patients being cerebral hemorrhage, and that in the elderly patients being cerebral infarction. The 20-year survival rate was 39.9% and its 95% confidence interval was (28.4%, 51.4%). Nineteen cases were indicated for neurovascular surgical operation, accounting for 26.6% of the 72 patients. Conclusions In the long-term follow-up study, about one third of the patients had the recurrent TIA. The occurrence rate of complete stroke was markedly higher than that of myocardial infarction. Presumably, the effect of neurovascular surgical operation on the prevention of complete stroke in patients with TIA is limited.