Paper Offer # 05P-660 Assessment of Corrosivity Associated with Exhaust Gas Recirculation in a Heavy-Duty Diesel Engine Michael D. Kass, John F. Thomas, Dane Wilson, and Samuel A. Lewis, Sr. Oak Ridge National Laboratory Andy Sarles Virginia Polytechnic Institute and State University Copyright © 2004 SAE International ABSTRACT A high-resolution corrosion probe was placed within the airhorn section of the exhaust gas recirculation (EGR) loop of a heavy-duty diesel engine. The corrosion rate of the mild-steel probe elements was evaluated as a function of fuel sulfur level, EGR fraction, dewpoint margin, and humidity. No significant corrosion was observed while running the engine using a No. 2 grade, < 15ppm sulfur diesel fuel; however, high corrosion rates were observed on the probe elements when operating the engine using a standard grade No. 2 diesel fuel (~350 ppm sulfur) while condensing water in the EGR loop. The rate of corrosion on the mild steel elements was found to increase with increasing levels of sulfate in the condensate. However, the engine conditions influencing the sulfate level were not clearly identified in this study. INTRODUCTION BACKGROUND Exhaust gas recirculation (EGR) is being used as a means of lowering NOx emissions from heavy duty diesel engines. During this process, a portion of the exhaust is recirculated back to the cylinder (via the intake manifold) where the exhaust gas acts as a diluent. This lowers combustion temperature which reduces the formation of nitrogen oxides (NOx). EGR is currently used to meet on-highway NOx emissions for Tier 3 emission levels for heavy-duty diesel engines. Very high levels of EGR have been shown to push combustion to low temperature regimes where both NOx and PM levels are low. This is currently an area of intense study. During the combustion of diesel fuel, corrosive gases containing sulfur and nitrogen are produced. With EGR these corrosive gases are returned to the intake manifold where ambient conditions (such as temperature and humidity) and coolant conditions are believed to play a critical role in the formation of highly corrosive acidic compounds, especially sulfuric acid (1,2). Development of an in-situ measurement system would significantly advance the understanding of the corrosion potential associated with EGR, thereby enabling engine manufacturers to establish boundary conditions on engine operation to avoid high levels of corrosion. SULFURIC ACID FORMATION During the combustion of sulfur-bearing fuel with excess air, most of the sulfur is converted into gaseous SO 2 or absorbed into the particulate matter (PM) emissions. A small fraction is also converted into gaseous SO 3 (1-4). Sulfuric acid is primarily formed in diesel exhaust by a two-step process. In the first step gaseous SO 2 reacts with oxygen in the exhaust to form SO 3 which is described as follows: 2SO 2 + O 2 J 2SO 3 The SO 3 subsequently reacts with moisture in the exhaust to form sulfuric acid according to the following reaction: 2SO 3 + H 2 O J H 2 SO 4 Under typical exhaust conditions sulfuric acid will condense near temperatures approaching 150 o C while water condensation will occur at temperatures close to 25-30 o C (1-4). PROBE DESCRIPTION The corrosion probe used in this study is an electrical resistance (ER) based probe manufactured by Cormon Ltd. The probe uses their proprietary CEION technology to enable high resolution measurement (< 1micron) at relatively high sample rates (up to 0.25 Hz). A photograph showing the probe tip is shown in Fig. 1. The overall diameter of the probe is 2.54 cm and