Dual fuel engines use liquefied natural gas (LNG) as fuel, and there are risks that are not found in conventional diesel engines. A system for preventing explosion accidents is being applied to deal with the risk factors; thus, in this study the gas flow of explosion accident occurring in the charge air manifold was analyzed. When the explosion accident occurred in the charge air manifold, the characteristics of pressure rise and flame propagation were analyzed. As a countermeasure, the installation position and quantity of the explosion relief valve were analyzed. In the case of installing one explosion relief valve, it was impossible to deal with the explosion accident because the pressure exceeded the safety pressure. However, in the case of installing two explosion relief valves, the pressure did not exceed the safety pressure. It was considered suitable to install two explosion relief valves at the charge air inlet and the closed end position to prevent demages from explosion accidents in the charge air manifold of the dual fuel engine.

In selective catalytic reduction (SCR) systems, urea-water solution (UWS) is injected upstream of the catalyst, where water evaporation, urea thermolysis, and isocyanic acid (HNCO) hydrolysis release the NH₃ required for NO_x reduction. Data at pressures of tens of bar combined with rapid temperature variation remain scarce. This study numerically evaluates the evaporation, decomposition, and NH₃ formation potential of UWS sprays in an engine-like, non-combusting transient thermal environment. A motoring direct injection diesel engine model, validated against measured in-cylinder pressure, gave a peak mass-averaged temperature of about 851 K. A three-dimensional CFD model coupling a multicomponent droplet evaporation model with gas-phase urea thermolysis and HNCO hydrolysis was applied to four injection quantities of 11.5, 23.2, 28.2, and 33.1 mg/cycle. UWS injection lowered the peak pressure and temperature through the endothermicity of water evaporation and urea decomposition. The model predicted NH₃ conversion, referenced to the urea content of the injected UWS, and decreased monotonically from about 43% to 17% as the injection quantity increased, while the wall film residue rose from 1% to 31% of the injected mass. Because deposit-forming side reactions are not included and high-pressure species formation was not independently validated, these values represent an upper bound of the model-predicted formation potential. The predicted NH₃, therefore, represents a formation potential under non-firing conditions rather than an exhaust-gas concentration, since NH₃ formed in the cylinder would be largely oxidised at firing temperatures.