In-cylinder charge stratification and fuel-air mixing in a new, low-emission two-stroke engine

Abstract

A new air-assisted injection system-based two-stroke engine has been developed at the Indian Institute of Science, Bangalore over the past few years and shows the potential to meet emission norms such as Euro II and Euro III and yet deliver satisfactory performance. The 70 cc engine works on the direct mixture injection principle with scavenging performed by air alone instead of an air-fuel mixture. A small 20 cc pump driven off the engine is used for mixture preparation prior to in-cylinder injection of the mixture. In the present study, the mixture injection and subsequent charge stratification process inside the engine cylinder is modelled. A three-dimensional compressible flow code with a standard k-ε turbulence model with wall functions is developed and used for this modelling. To account for the moving boundary or piston in the engine cylinder domain, a non-stationary and deforming grid is used in this region with stationary cells in the ports and connecting ducts. A flux conservation scheme is used in the domain interface to allow the in-cylinder moving mesh to slide past the fixed port meshes. The initial conditions for flow parameters are taken from the output of a three-dimensional scavenging simulation. The state of the inlet charge is obtained from a separate modelling of the air-assisted injection system of this engine. The simulation results show that a large, near-stoichiometric region is present at most operating conditions in the cylinder head plane. The state of the in-cylinder charge at the onset of ignition is studied, leading to a good understanding of the mixing process. In addition, the sensitivity of two critical parameters in the mixing and stratification is investigated. The suggested parameters substantially enhance the flammable proportion at the onset of combustion. The predicted pressure-crank angle history from a combustion simulation supports this recommendation.

Advanced modern low-emission two-stroke cycle engines

“…On small-capacity engines the directinjection system application can substantially increase the engine unit cost, making production viability questionable. In order to address the high emission levels of current two-stroke engines, significant interest in direct-injection systems have been shown in India for application to two-stroke and four-stroke motorcycles [16][17][18]. Bajaj launched the first gasoline direct-injection two-stroke engine rickshaw in 2007 [19].…”

Simulation and experimental investigation of swirl-loop scavenging in two-stroke diesel engine with two poppet valves

“…In two-stroke engines, scavenging performance may be affected by engine speed and load. 43,44 Therefore, the influence of different speeds and loads on SLS performance should be simulated and analyzed. At the same time, on the condition that the scavenging pressure is constant, the scavenging performance parameters under different speeds and loads are measured.…”

PFI System for Retrofitting Small 4-Stroke Gasoline Engines

“…Meanwhile, GDI system has been found to emit higher numbers of particulates than PFI system [9]. Moreover, GDI system equipped best for 2-stroke engine because of its potential to control direct loss of mixture during scavenging phase while PFI system best for 4-stroke engine [10][11][12][13]. The PFI system as a fuelling system for internal combustion engine is shown in Fig.…”