The effect of turbo-charging and intercoolingon emissionsgeneration [i.e. intercooling on emissions generation] and durability of a diesel engine

[摘要] ENGLISH ABSTRACT:To reduce exhaust gas emissions in diesel engines and for engine upgrade purposes themajor parameters and equipment that should be looked at are boost pressure, intakecharge temperature, combustion chamber design and fuel injection equipment. Boostpressure is governed by the turbo-charger; with high-efficiency variable geometry turbochargers,effective control is possible to increase airflow rate at all operating conditionsof the engine. Efficient air-to-air inter-cooling results in the engine being filled with acooler air charge that will influence engine durability and heat rejection to the coolingsystem. The main objective of the investigation is to look at the influence of boostpressure and intake charge temperature on diesel combustion to better understand theprocesses where boost pressure is increased and intake charge temperature reduced toincrease the brake mean effective pressure of the engine and reduce emissions generation.By running an engine at different intake boost pressures and intake charge temperatures a25-point matrix was formed at three different operating conditions. On completion of theengine testing, data processing and data evaluation, a number of important conclusionswere made about the behaviour of the engine running under different conditions. Thisenabled the researcher to understand how boost pressure and intake charge temperatureinfluence engine power output, fuel consumption, engine durability and exhaust gasemissions. The opinion is proved when, in most cases, the 75 test points were used tobuild multiple linear regression models to determine which engine parameters (dependentvariables) have a significant effect on emissions generation and durability parameters.From the data it is evident that boost pressure has a positive influence on most engineparameters, as an increase in boost pressure results in an increase in air mass flowthrough the engine. An increase in air mass flow reduces combustion chamber gastemperature as the result of an increase in excess air ratio during combustion.A further result of the increase in excess air ratio is that less soot is formed during thefirst part of combustion and more soot and partly decomposed Hydrocarbon (HC)compounds are oxidised during the late combustion phase. Therefore, with an increase inboost pressure, Bosch smoke emissions reduce, but with a change in intake airtemperature no difference in smoke concentration is seen except at the very low boostpressure and very high boost temperature test points where low air/fuel ratios exist andthe slight increase in air-flow rate as a result of lower air inlet temperature has a biginfluence.Nitric Oxide (NO) emissions, on the other hand, are more dependent on intake airtemperature than on boost pressure, which was proved in the multiple regressionsmodelling performed on the test data. The flame zone and the post-flame zonetemperature play the dominant role in NO formation. As explained in the resultsdiscussion on NO formation, intake air temperature influences the ignition mixturetemperature and the subsequent flame zone temperature. A lower intake air conditionresults in longer ignition delay and increases the initial rate of combustion.

[发布机构] Stellenbosch University