The Potential of SNCR Based NOx Reduction in a Double Compression Expansion Engine

Abstract

Selective Non-Catalytic Reduction (SNCR), used to reduce the emissions of nitrogen oxides (NOx), has been a well-established technology in the power plant industry for several decades. The SNCR technique is an aftertreatment strategy based on thermal reduction of NOx at high temperatures. In the compression ignition engine application, the technology has not been applicable due to low exhaust temperatures, which makes the SCR (Selective Catalytic Reduction) system essential for efficient nitrogen oxide reduction to fulfill the environment legislation. For a general Double Compression Expansion Engine (DCEE) the complete expansion cycle is split in two separate cycles, i.e. the engine is a split cycle engine. In the first cylinder the combustion occurs and in the second stage the combustion gas is introduced and further expanded in a low-pressure expansion cylinder. The combustion cylinder is connected with the expansion cylinder through a large insulated high-pressure tank. If an ammonia based solution is injected after the combustion cylinder, the residence time and high gas temperature in the high-pressure tank allows the Selective Non-Catalytic Reduction mechanisms to ensue. In this paper, AUS 32 vaporization efficiency was studied by injection droplet distribution measurements and CFD simulations. The Selective Non-Catalytic Reduction concept was evaluated utilizing a 1D GT-SUITE model of a potential DCEE concept where the SNCR based mechanisms were added. Engine speed, normalized stoichiometric ratio (NSR), load and air-fuel excess ratio were swept in the 1D simulation process. The simulation results suggest efficient vaporization of AUS 32 and the presence of SNCR mechanisms in the Double Compression Expansion Engine's medium and high load operating points was verified with conversion efficiency above 50 % in some of the simulation cases for NSR = 1 and close to 80-100 % for NSR = 2 and NSR = 3 when the exhaust gas temperature from the combustion cylinder was in the optimal range for SNCR based reactions. (Less)