Effect Of Charge Stratification Research Articles

Numerical investigation of stratified air/fuel preparation in a GDI engine

A numerical study has been performed to study atomization and preparation of air/fuel mixture under Gasoline Direct Injection (GDI) conditions. Performance of a single-hole injector was initially investigated and effects of ambient pressure, temperature and temperature of the injected fuel on liquid and vapour penetration lengths were analysed. Subsequently, air/fuel mixture preparation for a multi-hole injector in a simplified GDI engine was investigated. To simulate part load engine conditions, fuel spray and mixing was studied during the compression stroke of the engine. Effect of charge stratification, wall wettability and droplet statics on engine operating conditions like start of injection, injection pulse width, charge inlet temperature, engine RPM and overall equivalence ratio was studied. The droplet phase was tracked using Lagrangian framework and the continuous phase was simulated within the Eulerian framework. Turbulence modelling was performed using the standard k−ε model and ideal gas law was assumed while performing vapour-liquid equilibrium calculations.

Numerical Simulation of the Effects of Charge Stratification on Combustion and Emissions

A fully coupled multidimensional computational fluid mechanics and reduced chemical kinetics model is adopted to investigate the effects of charge stratification on combustion and emissions. Seven different kinds of imposed stratification have been introduced according to the position of the maximal local fuel/air equivalence ratio in the cylinder at intake valve close. The results show that the charge stratification results in stratification of the in-cylinder temperature. The former four kinds of stratification, whose maximal local equivalence ratios locate between the cylinder center and half of the cylinder radius, advance ignition timing, reduce the pressure-rise rate, and retard combustion phasing. But the following three kinds of stratification, whose maximal local equivalence ratios appear between half of the cylinder radius and the cylinder wall, have little effect on the cylinder pressure. For the two discussed equivalence ratios, all kinds of stratification can reduce unburned fuel emissions; a...

Local mixture injection to extend the lean limit of spark-ignition engines

The effect of charge stratification by direct, in-cylinder injection of a small quantity of propane-air mixture in a single-cylinder, propane-fuelled, spart-ignition engine, has been determined in terms of in-cylinder pressure, flame visualisation and exhaust emissions. The operating conditions ranged from low load to wide open throttle at 1000 and 1500 rpm, and with quiescent and swirling in-cylinder flows. The effects of injection-driven flow and turbulence on combustion have been considered independently of mixture strength by assessing the consequences of injecting a local mixture of an equivalence ratio equal to that of the port-induced charge.

Charge Stratification in a Spark Ignition Engine

The effect of charge stratification on lean mixture combustion in a Ricardo E6 single-cylinder four-stroke reciprocating engine has been investigated. To do this, a commercially available spark plug was modified so that small amounts of pure methane gas could be injected, via the spark electrode, into a lean mixture within the combustion chamber prior to ignition. The effect on engine performance of variations in the methane injection process were analysed. The research has led to the following conclusions: 1. The lean limit of a homogeneous air-fuel mixture is extended by this relatively simple charge stratification process. 2. The effectiveness of charge stratification is most noticeable at lean air-fuel ratios in terms of improved brake specific fuel consumption. 3. Unburnt hydrocarbon emission levels are higher with the stratified charge process when compared to normal homogeneous mixture operation. 4. Carbon monoxide levels with stratified charge combustion are almost the same or a little lower than normal operation at the leanest air-fuel ratios.