Amin Maghbouli

Parametric Comparison of Well-Mixed and Flamelet n-dodecane Spray Combustion with Engine Experiments at Well Controlled Boundary Conditions

Extensive prior art within the Engine Combustion Network (ECN) using a Bosch single axial-hole injector called ‘Spray A’ in constant-volume vessels has provided a solid foundation from which to evaluate modeling tools relevant to spray combustion. In this paper, a new experiment using a Bosch three-hole nozzle called ‘Spray B’ mounted in a 2.34 L heavy-duty optical engine is compared to sector-mesh engine simulations. Two different approaches are employed to model combustion: the ‘well-mixed model’ considers every cell as a homogeneous reactor and employs multi-zone chemistry to reduce the computational time. The ‘flamelet’ approach represents combustion by an ensemble of laminar diffusion flames evolving in the mixture fraction space and can resolve the influence of mixing, or ‘turbulence-chemistry interactions,’ through the influence of the scalar dissipation rate on combustion. Both combustion methodologies are implemented in the Lib-ICE code which is an unsteady Reynolds-averaged Navier-Stokes solver with k-ɛ turbulence closure based on OpenFOAM® technology. Liquid length and vapor penetration predictions generally fall within the experimental measurement uncertainty at 7.5% O2, 900 K, and 15.2 kg/m3. Flame liftoff length, cylinder pressure, apparent heat release rate, and ignition delay time from the two computations are compared to experiments under single parametric variation of ambient density 15.2 kg/m3 and 22.8 kg/m3, temperatures of 800, 900, and 1000 K, at 13, 15 and 21% Oxygen and injection pressure of 500, 1000, and 1500 bar. Both models generally provide apparent heat release rate maxima to within the uncertainty. The flamelet model better predicts the sensitivity of lift-off length while the well-mixed model better predicts ignition delay.

Numerical investigation of PPCI combustion at low and high charge stratification levels

Partially premixed compression ignition combustion is one of the low temperature combustion techniques which is being actively investigated. This approach provides a significant reduction of both soot and NOx emissions. Comparing to the homogeneous charge compression ignition mode, PPCI combustion provides better control on ignition timing and noise reduction through air- fuel mixture stratification which lowers heat release rate com- pared to other advanced combustion modes. In this work, CFD simulations were conducted for a low and a high air-fuel mixture stratification cases on a light-duty optical engine operating in PPCI mode. Such conditions for PRF70 as fuel were experimentally achieved by injection timing and spray targeting at similar thermodynamic conditions. After validating the computed results of cylinder pressure, apparent heat release rate, and OH ∗ spatial distributions, differences in engine thermal load and mixture fraction distributions at first stage and second stage ignition were compared. Assuming similar second stage ignition timing which is provided by intake air heating, experimental and simulation results reveal that the time between first and second stage ignition shortens and combustion phases to the main stage ignition faster in the high stratification case. Using flame structure diagrams, this was attributed to availability of a larger range of mixture fractions with higher reactivity. Creating optimum air-fuel stratification then can be considered as a useful and additional controlling parameter for a PPCI engine combustion phasing and subsequent emission formation.

Experimental Study on the Combustion Process and Performance of Diesel Engines Fueled by Emulsion Diesel With Novel Organic Additives

Transportation is one of the major contributors to the world’s energy consumption and greenhouse gases emissions. The need for increased efficiency has placed diesel engine in the spotlight due to its superior thermal efficiency and fuel economy over gasoline engine. However, diesel engines also face the major disadvantage of increased NOx emissions. To address this issue, three types of emulsion fuels with different water concentrations (5%, 10% and 15% mass water) are produced and tested. Novel organic materials (glycerin and ployethoxy-ester) are added in the fuel to provide extra oxygen for improving combustion. NP-15 is added as surfactant which can help to reduce the oil and water surface tension, activates their surface, and maximizes their superficial contact areas, thereby forming a continuous and finely dispersed droplets phase. The stability of the emulsion fuels is tested under various environmental temperature for one year, and no significant separation is observed. It is better than normal emulsion fuel which can only maintain the state for up to three months. The combustion process and performance of the emulsion fuels are tested in a four-stroke, four cylinder diesel engine. The results indicate that the water droplets enclosed in the emulsion fuel explode at high temperature environment and help to break up the big oil droplets into smaller ones, thereby significantly increase the surface area of the oil droplets and enhance the heat transfer from hot gas to the fuel. As a result, the fuel evaporation is improved and the combustion process is accelerated, leading to an improved brake thermal efficiency (up to 14.2%). Meanwhile, the presence of the water causes the peak temperature of the flame to drop, thereby significantly bringing down the NOx emissions by more than 30%.Copyright