Search Results

A combustion bomb has been developed which allows simulation of diesel combustion without the need to heat the bomb to high temperatures. Simulation of the compression stroke is achieved by burning a lean precharge composed of acetylene, oxygen and nitrogen. By controlling the initial partial pressures of these constituents it is possible to burn them to a state with an oxygen concentration, temperature and pressure representative of conditions in a diesel engine at the start of fuel injection. Diesel fuel injected into these gases autoignites and burns in a manner typical of combustion in diesel engines. This paper describes the design and operation of such a bomb. Experimental results are presented to illustrate its salient features. Particular attention is devoted to various means of obtaining optical access to the flow and the advantages offered over rapid compression machines or heated bombs.

A turbulent entrainment model for the turbulent combustion process in spark-ignition engines is described. The model uses the basic quantities of turbulent flow; i.e. the integral length scale, micro length scale, and turbulent intensity. The characteristic reaction time for a large eddy τ is calculated using the characteristic reaction time τc for the microscale, λ/S ℓ, where S ℓ is the laminar flame speed and propagation of ignition sites within a coherent turbulent structure. τ is related to the flame kernel development time and shows similar trends to the ignition delay time. The combustion model is demonstrated by calculations showing the typical trend behavior of combustion duration with equivalence ratio, exhaust gas recirculation, spark timing and engine speed.

During combustion in a diesel engine radiation heat transfer is the same order of magnitude as the convection heat transfer. Therefore for a reliable engine simulation the radiation transfer equation should be solved simultaneously with the flow and energy equations. A rigorous solution for the radiative transfer is, however, neither warranted nor cost effective. An approximation is needed at a level consistent with those used in modeling the fuel spray, the chemical kinetics, the soot and the turbulence. The approximation should account for the anisotropic behavior of radiation in the engine and be easily integrated into finite difference codes. This paper illustrates use of the first and the third order spherical harmonics approximation to the radiative transfer equation and the delta-Eddington approximation to the scattering phase function for droplets in the flow.

Measurements were made of exhaust histories of the following species: unburned hydrocarbons (HC), carbon monoxide, carbon dioxide, oxygen, and nitric oxide (NO). The measurements show that the exhaust flow can be divided into two distinct phases: a leading gas low in HC and high in NO followed by a trailing gas high in HC and low in NO. Calculations of time resolved equivalence ratio throughout the exhaust process show no evidence of a stratified combustion. The exhaust mass flow rate is time resolved by forcing the flow to be locally quasi-steady at an orifice placed in the exhaust pipe. The results with the quasi-steady assumption are shown to be consistent with the measurements. Predictions are made of time resolved mass flow rate which compare favorably to the experimental data base. The composition and flow histories provide sufficient information to calculate the time resolved flow rates of the individual species measured.