TS-152
A Study on Effects of Recirculated Exhaust Gas upon Engine Wear in Diesel Engines
Myung-whan BAE*, Kazuo TSUCHIYA** and Kwang-sun KIM***
ABSTRACT
The effects of recirculated exhaust gas on the wear of cylinder liner, piston and piston rings were investigated by the experiment with a two-cylinder, four cycle, indirect injection marine diesel engine operating at an engine load of 75% and an engine speed of 1600 rpm. For the purpose of comparison between the wear rates of the two cylinders with and without EGR, the recirculated exhaust gas was sucked into one of two cylinders after the soot in exhaust emissions was removed by an intentionally designed cylinder-type scrubber equipped with 6 water injectors, while only the fresh air was inhaled into the other cylinder. It was found that firstly the mean wear rate of cylinder liner with EGR was greater in the measurement positions of the second half than of the first half, and that the mean wear rate without EGR was almost uniform regardless of measurement positions. Secondly, the wear rate of piston skirt with EGR increased a little bit, but the piston head diameter increased, rather than decreased, owing to soot adhesion and erosion wear, and especially larger with EGR. Finally, the wear rates of the top and second piston rings( compression ring) thickness with EGR were more than twice the wear rate of top ring in case of no EGR, but the wear rate of oil rings thickness without EGR increased greater than that with EGR.
Key Words : EGR(Exhaust Gas Recirculation), Cylinder Liner, Piston Ring, Diesel Engine, Wear Rate, Soot Adhesion, Erosion wear
1. INTRODUCTION
Recently atmospheric environment has been heavily polluted by exhaust gases emitted from combustion engines. Since problems of air pollution are mainly attributed, in particular, to exhaust emissions of diesel engines, there have been many research efforts among the concerned industries and institutions to work on solutions to reduce hazardous emissions from diesel engines. (1) One of these measures to reduce NOx emissions is EGR method, which produces a remarkable NOx reduction effect. It is well documented, however, that EGR may increase other exhaust emissions, fuel consumption rate and the wear of engine components such as the piston ring, cylinder liner, piston and other parts. In spite of these disadvantages, on the other hand, many researchers have been trying to apply the EGR system in a diesel engine because there are virtually no other better measures for NOx emissions reduction without a special reconstruction of engine. (2-4)
Bae et al. (3,4) have conducted experiments with EGR system mounted on a diesel engine in order to investigate its effect on exhaust emissions and fuel consumption rate, with the result that increased EGR rate at a high load and high speed led to excessive soot emissions, rendering the operation impractical. As an alternative, Bae et al. (5) have reported a substantial soot reduction effect by applying an exhaust gas recirculating system with scrubber that fed soot-removed exhaust gas back into the diesel engine.
In EGR application, the major research targets with regard to its effect on the wear increase are; increased soot amount adhered onto oil film (6,7); sulfuric contents contained in fuel (8〜10), and so on. While earlier studies were largely focused on abrasive wear due to soot(6), recent studies have been devoted mostly to study on wear due to SOx such as the deterioration of lubricating oil by SOx in recirculated exhaust gas(11) and the breaking of oil film due to H2SO4 generated from SOx.(12)97 〜 98% of sulfuric contents contained in fuel react with oxygen during combustion to make SO2, which is emitted included in exhaust gas. When EGR system is applied to recirculate some of the exhaust gas into the cylinders, the generated SO2 oxidizes into SO3, which reacts with water to make H2SO4.
* School of Transport Vehicle Engineering, Gyeongsang National University, 900, Gajwadong, Chinju, Gyeongnam, 600-701 Korea
TEL :+82-591-751-6071, FAX :+82-591-762-0227
E-mail : mwbae@nongae.gsnu.ac.kr
** Meiji University in Japan
*** Korea University of Technology and Education
