A simplified method for the computation of the premixed mode heat release in di diesel engines.

Abstract

Diesel engines have a wide spread of mobility applications and a solid reputation of high efficiency, low fuel consumption and reliability. The most challenging demand for its further development are the simultaneous reductions on fossil fuel consumption and pollutant emissions induced by an ever strict legislation scenario. High precision digitally controlled fuel injection systems and real time engine control strategies based on in-cylinder pressure control could contribute for the achievement of the low emissions goal. One aspect with particular interest regarding the engine control is to limit the premixed phase diesel combustion. Near stoichiometric fuel-air mixture is rapidly burned at high temperatures in the premixed mode, causing engine vibration, noise and nitrogen oxides emissions. In the current work, a methodology is developed for the rapid determination of the premixed mode combustion total heat release. It is based in the direct interpolation of the gross heat release curve by a single Wiebe function, which after some manipulation demands the solution of two trivial equations for the premixed combustion angle and total heat released in premixed mode, besides a nonlinear equation for determining the premixed mode form factor. In order to establish a precision benchmark, a detailed program using quasi-Newton minimization and finite-difference gradient was also employed to approximate the experimental heat release data by two Wiebe functions, according to Miyamoto's model. The proposed methodology and the baseline detailed interpolation routine were applied to approximate experimental data from a turbocharged DI diesel engine operating in three distinct engine operational conditions; low, mid and full load. According to the obtained results, the simplified method proposed here has shown to be around 20 times faster than the benchmark detailed program, with a precision loss of only up to 1% for all tested regimes.