Search Results

This paper presents a comparison of the influence of different mixture preparation strategies on gaseous fuel combustion in SI engines. Three mixture preparation strategies are presented for a dedicated LPG fuelled engine, showing varying results - gaseous phase port injection (PFI-G), liquid-phase port injection (PFI-L) and gaseous-phase throttle-body injection (TBI-G). Previous work by the authors has shown considerable differences in emissions and thermal efficiency between different fuelling strategies. This paper extends this work to the area of combustion characteristics and lean limit operation and closer analyses the differences between these systems. A dedicated LPG in-line six cylinder engine with compression ratio increased to 11.7:1 (up from the standard 9.65:1) was tested over a range of speed/torque conditions representing most of the steady-state parts of the Euro drive-cycle for light duty-vehicles. The air-fuel ratio was varied from lambda 1.0 to the lean limit.

Gas assisted jet ignition is a prechamber combustion initiation system for conventional spark ignition engines. With the system, a chemically active turbulent jet is used to initiate combustion in lean fuel mixtures enabling reliable combustion over a much broader range of air-fuel ratios. The extended range is due to the distributed ignition source provided by the jet, which can overcome the problems of poorly mixed main chamber charges and slower burning fuels. In addition, the ability to reliably ignite lean mixtures improves the thermal efficiency and enables ultra low emission levels. Experiments together with flame propagation modeling completed using STAR-CD with CHEMKIN Kinetics were done in order to examine the effects of numerous prechamber fuels on the ignition of the main fuel, which consisted of either liquefied petroleum gas (LPG) or gasoline.

This paper presents the experimental results of a new look at throttle body injection (TBI) for LPG, targeting the same objectives as fourth generation LPG systems. The TBI system is configured from CFD studies to minimize cylinder-to-cylinder air-fuel variations, enabling the lean limit to be extended as far as lambda 1.6. An in-line, six-cylinder engine with a compression ratio of 11.7:1 (up from the standard 9.65:1) over a range of speed/torque conditions was utilized, with the air/fuel ratio varied from lambda 1.2 to 1.6. Additionally, cylinder-to- cylinder air-fuel variations were measured over a range of speeds and throttle positions representing most of the steady state parts in the Euro drive-cycle for light-duty vehicles. It is shown that mixing characteristics have a considerable effect on emissions and thermal efficiency.

The variability of in-cylinder combustion of gasoline at idle has been investigated previously, culminating in the development of a model relating the past and future indicated torque deviations from the mean at given engine operating conditions of intake manifold pressure, engine speed and spark advance. The developed model has the potential to be used in an idle speed control algorithm to improve vehicle noise vibration and harshness (NVH) at low engine speeds and loads. While environmental considerations have spawned the development of liquefied petroleum gas (LPG) as a viable alternative fuel, adaptation of the variability model to multipoint LPG injected automotive engines is complicated by the fact that the fuel mixture concentrations of propane and butane are subject to wide variations depending on a variety of factors including geographic location and local market pricing.