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The high-pressure isobaric combustion has been proposed as the most suitable combustion mode for the double compre4ssion expansion engine (DCEE) concept. Previous experimental and simulation studies have demonstrated an improved efficiency compared to the conventional diesel combustion (CDC) engine. In the current study, isobaric combustion was achieved using a single injector with multiple injections. Since this concept involves complex phenomena such as spray to spray interactions, the computational models were extensively validated against the optical engine experiment data, to ensure high-fidelity simulations. The considered optical diagnostic techniques are Mie-scattering, fuel tracer planar laser-induced fluorescence (PLIF), and natural flame luminosity imaging. Overall, a good agreement between the numerical and experimental results was obtained.

The focus of this study is to aid the development of the isobaric combustion engine by investigating multiple injection strategies at moderately high pressures. A three-dimensional (3D) commercial computational fluid dynamics (CFD) code, CONVERGE, was used to conduct simulations. The validation of the isobaric combustion case was carried out through the use of a single injector with multiple injections. The computational simulations were matched to the experimental data using methods outlined in this paper for different multiple injection cases. A sensitivity analysis to understand the effects of different modeling components on the quantitative prediction was carried out. First, the effects of the kinetic mechanisms were assessed by employing different chemical mechanisms, and the results showed no significant difference in the conditions under consideration.

In the study presented in this paper, experimental data from a pneumatic hybrid has been compared to the results from a simulation of the engine in GT-Power. The engine in question is a single-cylinder Scania D12 diesel engine, which has been converted to work as a pneumatic hybrid. The base engine model, provided by Scania, is made in GT-Power and it is based on the same engine configuration as the one used during real engine testing. During pneumatic hybrid operation the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration and during vehicle acceleration the engine can be operated as a 2-stroke air-motor driven by the previously stored pressurized air. There is also a possibility to use the stored pressurized air in order to supercharge the engine when there is a need for high torque, like for instance at take off after a standstill or during an overtake maneuver.

Ion current measurements can give information useful for controlling the combustion stability in a multi-cylinder engine. Operation near the dilution limit (air or EGR) can be achieved and it can be optimized individually for the cylinders, resulting in a system with better engine stability for highly diluted mixtures. This method will also compensate for engine wear, e.g. changes in volumetric efficiency and fuel injector characteristics. Especially in a port injected engine, changes in fuel injector characteristics can lead to increased emissions and deteriorated engine performance when operating with a closed-loop lambda control system. One problem using the ion-current signal to control engine stability near the lean limit is the weak signal resulting in low signal to noise ratio. Measurements presented in this paper were made on a turbocharged 9.6 liter six cylinder natural gas engine with port injection.

This article deals with study of ionization current sensing technique's signal characteristics while operating with pre-chamber spark plug to achieve plasma jet ignition in a 6 cylinder 9 liter turbo-charged natural gas engine under EGR and excess air dilution. Unlike the signal with conventional spark plug which can be divided into distinct chemical and thermal ionization peaks, the signal with pre-chamber spark plug shows a much larger first peak and a negligible second peak thereafter. Many studies in past have found the time of second peak coinciding with the time of maximum cylinder pressure and this correlation has been used as an input to combustion control systems but the absence of second peak makes application of this concept difficult with pre-chamber spark plug.

A control system for pneumatic variable valve actuation has been designed, implemented and tested in a single cylinder test engine with valve actuators provided by Cargine Engineering AB. The design goal for the valve control system was to achieve valve lifts between 2 and 12 mm over an engine speed interval of 300 to 2500 rpm. The control system was developed using LabView and implemented on the PCI 7831. The design goals were fulfilled with some limitations. Due to physical limitations in the actuators, stable operation with valve lifts below 2.6 mm were not possible. During the engine testing the valve lift was limited to 7 mm to guarantee piston clearance. Different valve strategies for residual gas HCCI combustion were generated on a single-cylinder test engine.

It has been proven that partially premixed combustion (PPC) has the capability of high combustion efficiency with low soot and NOx emissions, which meet the requirements of increasingly restricted emission regulations. In order to obtain more homogenous combustion and longer ignition delay in PPC, different fuel injection strategies were employed which could affect the fuel air mixing and control the combustion. In the present work, a light duty optical diesel engine was used to conduct high speed particle image velocimetry (PIV) for single, double and triple injections with different timings. A quartz piston and a cylinder liner were installed in the Bowditch configuration to enable optical access. The geometry of the quartz piston crown is based on the standard diesel combustion chamber design for this commercial passenger car engine, including a re-entrant bowl shape.

Earlier studies on efficiency improvement in CI engines have suggested that heat transfer losses contribute largely to the total energy losses. Fuel impingement on the cylinder walls is typically associated with high heat transfer. This study proposes a two-injector concept to reduce heat losses and thereby improve efficiency. The two injectors are placed at the rim of the bowl to change the spray pattern. Computational simulations based on the Reynolds-Averaged Navier-Stokes approach have been performed for four different fuel injection timings in order to quantify the reduction in heat losses for the proposed concept. Two-injector concepts were compared to reference cases using only one centrally mounted injector. All simulations were performed in a double compression expansion engine (DCEE) concept using the Volvo D13 single-cylinder engine. In the DCEE, a large portion of the exhaust energy is re-used in the second expansion, thus increasing the thermodynamic efficiency.