Implementation of the Partially Premixed Combustion concept in a 2-stroke HSDI diesel engine fueled with gasoline

Abstract

Partially Premixed Combustion (PPC) of fuels in the gasoline octane range has proven to combine low NOX and soot emissions with high indicated efficiencies, while still retaining control over combustion phasing with the injection event. Previous research performed in four-stroke engines, has shown how the operating region where gasoline PPC concept can be successfully implemented is largely linked to the octane number of the fuel, making difficult to cover the entire load range with a fixed fuel.In this framework, 2-stroke engines arise as a promising solution to extend the load range of gasoline PPC concept, since it intrinsically provides equivalent torque response with only half the IMEP required in a 4-stroke cycle. Moreover, 2-stroke architecture provides high flexibility on the air management parameters to substantially control the cylinder conditions and affect the combustion environment, allowing proper combustion control even in low load conditions. An experimental investigation has been performed to evaluate the potential of the PPC concept for pollutant control, using a commercial gasoline with Research Octane Number of 95 in a newly-designed 2-stroke poppet valves automotive diesel engine. The experimental results confirm how it is possible to achieve stable gasoline PPC combustion at a low speed medium load point (1200 rpm, 5 bar IMEP); with good combustion stability (σIMEP below 3%), high combustion efficiency (over 98%), and low NOX and zero soot levels; thanks to the wide control of the cylinder gas temperature provided by the air management settings. Nevertheless, in agreement to the results reported in the literature, the indicated cycle efficiency attained at this low load operating condition is lower than the obtained in conventional diesel combustion conditions. Therefore, a dedicated optimization process of the engine hardware and engine settings is required to fully exploit the benefits of gasoline PPC concept in the investigated 2-stroke engine architecture.

Experimental investigation of the influence of internal and external EGR on the combustion characteristics of a controlled auto-ignition two-stroke cycle engine

“…Numerous investigations have performed using exhaust port throttling to increase the amount of trapped residual gas in the combustion chamber [15,[30][31][32][33][34][35][36][37]. Duret et al developed this technique in an air-assisted direct fuel injection two-stroke engine using computational and numerical approaches [38][39][40].…”

Investigation on Multiple Injection Strategies for Gasoline PPC Operation in a Newly Designed 2-Stroke HSDI Compression Ignition Engine

“…Furthermore, the Homogeneous Charge Compression Ignition (HCCI) combustion concept with diesel fuel was implemented at low load conditions, and its potential for simultaneous reductions of NOX and soot emissions was experimentally proven [12]. However, the high reactivity of diesel fuel added to the intrinsically high residual gas fraction (IGR), characteristic of the scavenge loop architecture; made it impossible to attain a properly-phased combustion process even when using optimized hardware and engine settings [13]. Therefore, the application of HCCI in this 2-stroke engine concept was discarded.…”

Analysis of combustion concepts in a newly designed two-stroke high-speed direct injection compression ignition engine

“…26 However, the high reactivity of diesel fuel added to the high residual gas fraction (IGR) characteristic of the scavenge loop architecture, made it impossible to attain a properlyphased combustion even operating at low loads with optimized engine settings and hardware, so this combustion concept was discarded. 27 Nevertheless, the high flexibility in terms of air management settings to control the cylinder conditions and affect final combustion environment, also observed operating with CDC concept, 28 encouraged the authors to explore the potential of the PPC concept for pollutant control using a high octane fuel (RON95 gasoline) with a single injection strategy at medium-to-low load conditions. The compatibility of this concept with the 2-stroke configuration in terms of assuring precise control of the onset of combustion and stable PPC operation at low loads was demonstrated.…”

“…The compatibility of this concept with the 2-stroke configuration in terms of assuring precise control of the onset of combustion and stable PPC operation at low loads was demonstrated. 29 Recent research work extended the PPC operation to 5 bar and 3 bar of Indicated Mean Effective Pressure (IMEP), when using a single injection strategy with RON95 gasoline. Low NO X emissions (below 0.4 g/kWh) and zero soot emissions were obtained at these medium/low load conditions, while 98% of combustion efficiency and good combustion stability (covariance of the IMEP under 3%) was retained.…”