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Active prechamber combustion systems for SI engines represent a feasible and effective solution in reducing fuel consumption and pollutant emissions for both marine and ground heavy-duty engines. However, reliable and low-cost numerical approaches need to be developed to support and speed-up their industrial design considering their geometry complexity and the involved multiple flow length scales. This work presents a CFD methodology based on the RANS approach for the simulation of active prechamber spark-ignition engines. To reduce the computational time, the gas exchange process is computed only in the prechamber region to correctly describe the flow and mixture distributions, while the whole cylinder geometry is considered only for the power-cycle (compression, combustion and expansion). Outside the prechamber the in-cylinder flow field at IVC is estimated from the measured swirl ratio.

This paper investigates the FPGA resources for the implementation of in-cycle closed-loop combustion control algorithms. Closed-loop combustion control obtains feedback from fast in-cylinder pressure measurements for accurate and reliable information about the combustion progress, synchronized with the flywheel encoder. In-cycle combustion control requires accurate and fast computations for their real-time execution. A compromise between accuracy and computation complexity must be selected for an effective combustion control. The requirements on the signal processing (evaluation rate and digital resolution) are investigated. A common practice for the combustion supervision is to monitor the heat release rate. For its calculation, different methods for the computation of the cylinder volume and heat capacity ratio are compared. Combustion feedback requires of virtual sensors for the misfire detection, burnt fuel mass and pressure prediction.

Partially premixed combustion (PPC) is a promising way to achieve high thermal efficiency and low emissions, especially by using multiple injection strategies. The mechanisms behind PPC efficiency are still to be explained and explored. In this paper, multiple injections have been used to affect the gross indicated efficiency in an optical PPC engine modified from a Volvo MD13 heavy-duty diesel engine. The aim is both to improve and impair the gross indicated efficiency to understand the differences. The combustion natural luminosity is captured by a high-speed camera, and the distribution of fuel, oxygen, and temperature during the combustion process has been further explored by CFD simulation. The results show that with the right combination of the pilot, main, and post injection the gross indicated efficiency can be improved.

Dual-fuel engines for marine propulsion are gaining in importance due to operational and environmental benefits. Here the combustion in a dual-fuel marine engine operating on diesel and natural gas, is studied using a multiple high-speed camera arrangement. By recording the natural flame emission from three different directions the flame position inside the engine cylinder can be spatially mapped and tracked in time. Through space carving a rough estimate of the three-dimensional (3D) flame contour can be obtained. From this contour, properties like flame length and height, as well as ignition locations can be extracted. The multi-camera imaging is applied to a dual-fuel marine two-stroke engine, with a bore diameter of 0.5 m and a stroke of 2.2 m. Both liquid and gaseous fuels are directly injected at high pressure, using separate injection systems. Optical access is obtained using borescope inserts, resulting in a minimum disturbance to the cylinder geometry.

In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in a combustion mode dominated by ignition wave propagation. 3D-CFD modeling of such a combustion mode is challenging as the rate of fuel consumption can be dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of stratification in scalar concentration (enthalpy and reactant mass fraction) due to large scale turbulence on the propagation of reaction waves in PPC combustion engines. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane).

Partially Premixed Combustion (PPC) has shown to be a promising advanced combustion mode for future engines in terms of efficiency and emission levels. The combustion timing should be suitably phased to realize high efficiency. However, a simple constant model based predictive controller is not sufficient for controlling the combustion during transient operation. This article proposed one learning based model predictive control (LBMPC) approach to achieve controllability and feasibility. A learning model was developed to capture combustion variation. Since PPC engines could have unacceptably high pressure-rise rates at different operation points, triple injection is applied as a solvent, with the use of two pilot fuel injections. The LBMPC controller utilizes the main injection timing to manage the combustion timing. The cylinder pressure is used as the combustion feedback. The method is validated in a multi-cylinder heavy-duty PPC engine for transient control.

For the reduction of emissions and combustion noise in an internal combustion diesel engine, multiple injections are normally used. A pilot injection reduces the ignition delay of the main injection and hence the combustion noise. However, normal variations of the operating conditions, component tolerances, and aging may result in the lack of combustion i.e. pilot misfire. The result is a lower indicated thermal efficiency, higher emissions, and louder combustion noise. Closed-loop combustion control techniques aim to monitor in real-time these variations and act accordingly to counteract their effect. To ensure the in-cycle controllability of the main injection, the misfire diagnosis must be performed before the start of the main injection. This paper focuses on the development and evaluation of in-cycle algorithms for the pilot misfire detection. Based on in-cylinder pressure measurements, different approaches to the design of the detectors are compared.

In computational fluid dynamic simulations of partially premixed combustion engines it is common to find simplifications of the in cylinder flow conditions in order to save computational cost. One common simplification is to start the simulation at the moment of intake valve closing with an assumed initial flow condition, rather than making a full scavenging simulation. Another common simplification is the periodic sector assumption, limiting all sector cuts of the full cylinder to be identical periodic copies of each other. This work studies how such flow simplifications affect the spray injection and in turn the fuel/air mixing at different injection timings. Focus is put on the stratification of fuel concentration and gas temperature due to interaction of the spray, turbulence and piston geometry. The investigated engine setup consists of a light duty engine with a piston bowl and a five-hole injector.

In-cylinder heat losses in diesel engines decrease engine efficiency significantly and account for approximately 14-19% [1, 2, 3] of the injected fuel energy. A great part of the heat losses during diesel combustion presumably arises from the flame impingement onto the piston. Therefore, the present study investigates the heat losses during flame impingement onto the piston bowl wall experimentally. The measurements were performed on a full metal heavy-duty diesel engine with a small optical access through a removed exhaust valve. The surface temperature at the impingement point of the flame was determined by evaluating a phosphor’s temperature dependent emission decay. Simultaneous cylinder pressure measurements and high-speed videos are associated to the surface temperature measurements in each cycle. Thus, surface temperature readings could be linked to specific impingement and combustion events.

The natural gas/diesel dual-fuel engine is an interesting technique to reduce greenhouse gas emission. A limitation of this concept is the emission of un-combusted methane. In this study we analyzed the influence of PFI gas-injection timing on cylinder to cylinder gas-distribution, and the resulting methane emissions. This was done on a 6 cylinder HD engine test bench and in a GT-power simulation of the same engine. The main variable in all tests was the timing of the intake port gas injection, placed either before, after, or during the intake stroke. It showed that injecting outside of the intake window resulted in significant variation of the amount of trapped gaseous fuel over the 6 cylinders, having a strong impact on methane emissions. Injecting outside of the intake stroke results in gas awaiting in the intake port. Both testing and simulation made clear that as a result of this, cylinder 1 leans out and cylinder 6 enriches.

The double compression-expansion engine concepts (DCEE) are split-cycle concepts where the compression, combustion, expansion and gas exchange strokes occur in two or more different cylinders. Previous simulation studies reveal there is a potential to improve brake efficiency with these engine concepts due to improved thermodynamic and mechanical efficiencies. As a continuation of this project this paper studies an alternative layout of the DCEE-concept. The concept studied in this paper has three different cylinders, a compression, a combustion and an expansion cylinder. Overall system indicated and brake efficiency estimations were based on both engine experiments and simulations. The engine experiments were carried out at 10 different operating points and 5 fuelling rates (between 98.2 and 310.4 mg/cycle injection mass) at an engine speed of 1200 rpm. The inlet manifold pressure was varied between 3 and 5 bar.

The double compression expansion engine (DCEE) is a promising concept for high engine efficiency while fulfilling the most stringent European and US emission legislation. The complete thermodynamic cycle of the engine is split among several cylinders. Combustion of fuel occurs in the combustion cylinder and in the expansion cylinder the exhaust gases are over expanded to obtain high efficiency. A high-pressure tank is installed between these two cylinders for after-treatment purposes. One proposal is to utilize thermal reduction of nitrogen oxides (NOx) in the high-pressure tank as exhaust temperatures can be sufficiently high (above 700 °C) for the selective non-catalytic reduction (SNCR) reactions to occur. The exhaust gas residence time at these elevated exhaust temperatures is also long enough for the chemical reactions, as the volume of the high-pressure tank is substantially larger than the volume of the combustion cylinders.

Partially premixed combustion (PPC) in internal combustion engine as a low temperature combustion strategy has shown great potential to achieve high thermodynamic efficiency. Methanol due to its unique properties is considered as a preferable PPC engine fuel. The injection timing to achieve methanol PPC conditions should be set very close to TDC, allowing to utilize spray-bowl interaction to further improve combustion process in terms of emissions and heat losses. In this study CFD simulations are performed to investigate spray-bowl interaction for a number of different piston designs and its impact on the heat transfer and the overall piston performance. The validation case is based on a single cylinder heavy-duty Scania D13 engine with a compression ratio 15. The operation point is set to low load 5.42 IMEPg bar with SOI -3 aTDC.

In this article, a virtual sensor for the estimation of the injected pilot mass in-cycle is proposed. The method provides an early estimation of the pilot mass before its combustion is finished. Furthermore, the virtual sensor can also estimate pilot masses when its combustion is incomplete. The pilot mass estimation is conducted by comparing the calculated heat release from in-cylinder pressure measurements to a model of the vaporization delay, ignition delay, and the combustion dynamics. A new statistical approach is proposed for the detection of the start of vaporization and the start of combustion. The discrete estimations, obtained at the start of vaporization and the start of combustion, are optimally combined and integrated in a Kalman Filter that estimates the pilot mass during the vaporization and combustion. The virtual sensor was programmed in a field programmable gate array (FPGA), and its performance tested in a Scania D13 Diesel engine.

Double Compression Expansion Engine (DCEE) concepts are split-cycle concepts where the main target is to improve brake efficiency. Previous simulations work [1] suggests these concepts has a potential to significantly improve brake efficiency relative to contemporary engines. However, a high peak efficiency alone might be of limited value. This is because a vehicle must be able to operate in different conditions where the engine load requirements changes significantly. An engine’s ability to deliver high efficiency at the most frequently used load conditions is more important than peak efficiency in a rarely used load condition. The simulations done in this paper studies the efficiency at low, mid and full load for a DCEE concept proposal. Two load control strategies have been used, lambda and Miller (late intake valve closing) strategies. Also, effects from charge air cooling has also been studied.

Selective Non-Catalytic Reduction (SNCR), used to reduce the emissions of nitrogen oxides (NOx), has been a well-established technology in the power plant industry for several decades. The SNCR technique is an aftertreatment strategy based on thermal reduction of NOx at high temperatures. In the compression ignition engine application, the technology has not been applicable due to low exhaust temperatures, which makes the SCR (Selective Catalytic Reduction) system essential for efficient nitrogen oxide reduction to fulfill the environment legislation. For a general Double Compression Expansion Engine (DCEE) the complete expansion cycle is split in two separate cycles, i.e. the engine is a split cycle engine. In the first cylinder the combustion occurs and in the second stage the combustion gas is introduced and further expanded in a low-pressure expansion cylinder. The combustion cylinder is connected with the expansion cylinder through a large insulated high-pressure tank.

The focus has recently been directed towards the engine out soot from Diesel engines. Running an engine in PPC (Partially Premixed Combustion) mode has a proven tendency of reducing these emissions significantly. In addition to combustion strategy, several studies have suggested that using alcohol fuels aid in reducing soot emissions to ultra-low levels. This study analyzes and compares the characteristics of PM emissions from naphtha gasoline PPC, ethanol PPC, methanol PPC and methanol diffusion combustion in terms of soot mass concentration, number concentration and particle size distribution in a single cylinder Scania D13 engine, while varying the intake O2. Intake temperature and injection pressure sweeps were also conducted. The fuels emitting the highest mass concentration of particles (Micro Soot Sensor) were gasoline and methanol followed by ethanol. The two alcohols tested emitted nucleation mode particles only, whereas gasoline emitted accumulation mode particles as well.

Heat loss is one of the greatest energy losses in engines. More than half of the heat is lost to cooling media and exhaust losses, and they thus dominate the internal combustion engine energy balance. Complex processes affect heat loss to the cylinder walls, including gas motion, spray-wall interaction and turbulence levels. The aim of this work was to experimentally compare the heat transfer characteristics of a stepped-bowl piston geometry to a conventional re-entrant diesel bowl studied previously and here used as the baseline geometry. The stepped-bowl geometry features a low surface-to-volume ratio compared to the baseline bowl, which is considered beneficial for low heat losses. Speed, load, injection pressure, swirl level, EGR rate and air/fuel ratio (λ) were varied in a multi-cylinder light duty engine operated in conventional diesel combustion (CDC) mode.

Partially Premixed Combustion (PPC) is a promising combustion concept with high thermodynamic efficiency and low emission level, and also with minimal modification of standard engine hardware. To use PPC in a production oriented engine, the optimal intake charge conditions for PPC should be included in the analysis. The experiments in this paper investigated and confirmed that the optimal intake conditions of net indicated efficiency for PPC are EGR between 50% and 55% as possible and the lambda close to 1.4. Heat-transfer energy and exhaust gas waste-energy contribute to the majority of the energy loss in the engine. The low EGR region has high heat-transfer and low exhaust gas enthalpy-waste, while the high EGR region has low heat-transfer and high exhaust gas waste-enthalpy. The optimal EGR condition is around 50% where the smallest energy loss is found as a trade-off between heat transfer and exhaust-gas enthalpy-waste.

This article presents a study related to application of pre-chamber ignition system in heavy duty natural gas engine which, as previously shown by the authors, can extend the limit of fuel-lean combustion and hence improve fuel efficiency and reduce emissions. A previous study about the effect of pre-chamber volume and nozzle diameter on a single cylinder 2 liter truck-size engine resulted in recommendations for optimal pre-chamber geometry settings. The current study is to determine the dependency of those settings on the engine size. For this study, experiments are performed on a single cylinder 9 liter large bore marine engine with similar pre-chamber geometry and a test matrix of similar and scaled pre-chamber volume and nozzle diameter settings. The effect of these variations on main chamber ignition and the following combustion is studied to understand the scalability aspects of pre-chamber ignition. Indicated efficiency and engine-out emission data is also presented.