Flow Analysis and Theoretical Design of Diesel Engine Exhaust Port

Exhaust port is an important part of a diesel engine which affects the combustion and emission. It is important to have a good design for exhaust port. In this paper, the calculation formula of the optimal area ratio (K-opt) of outlet and inlet of exhaust port was derived. The formula shows that K-opt is only determined by relative pressure difference (RPD). Then influence of the area ratio (K) of outlet and inlet on flow capacity of exhaust port and the trend of K-opt with relative pressure difference were studied numerically to verify the validity and applicability of the formula. The numerical results shows that the mass flow rate increases first and then keeps constant with the increase of K at the same RPD. K-opt exists and decreases first and then keeps constant with the increase of RPD. The numerical trend is consistent with theoretical trend and the errors between maximum mass flow rates of numerical results and actual mass flow rates at theoretical optimal area ratios are all less than 5% meeting engineering accuracy. It is indicated that the derived formula is correct and applicable. When an exhaust port is designed, the outlet area can be estimated by this formula.