Using combustion net torque for estimation of combustion properties from measurements of crankshaft torque

• Two methods for torque based combustion property estimation are proposed.
• The concept of combustion net torque is connected to the burned mass fraction.
• Both the entire burned mass fraction and the 50% burned mass fraction are estimated.
• The 50% burned mass fraction estimates have a bias of less than 1 CAD.
• Standard deviations of the 50% burned mass fraction estimates are less than 2.7 CAD.

Two methods, both based on the concept of combustion net torque, for estimation of combustion properties using measurements of crankshaft torque data are investigated in this work. The first of the proposed methods estimates entire burned mass fraction traces from corresponding combustion net torque traces. This is done by solving a convex optimization problem that is based on a derived analytical relation between the two quantities. The other proposed estimation method estimates the well established combustion phasing measure referred to as 50% burned mass fraction directly from combustion net torque using a nonlinear black-box mapping. The methods are assessed using both simulations and experimental data gathered from a 5-cylinder light-duty diesel engine equipped with a crankshaft torque sensor and cylinder pressure sensors that are used for reference measurements. The results indicate that both methods work well but the method that estimates entire burned mass fraction traces is more sensitive to torque data quality. Based on the experimental crankshaft torque data, the direct combustion phasing estimation method delivers estimates with a bias of less than 1 CAD and a cycle-to-cycle standard deviation of less than 2.7 CAD for all cylinders.