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Alternative fuels, such as natural and bio-gas, are attractive options for reducing greenhouse gas emissions from combustion engines. However, the naturally occurring variation in gas composition poses a challenge and may significantly impact engine performance. The gas composition affects fundamental fuel properties such as flame propagation speed and heat release rate. Deviations from the gas composition for which the engine was calibrated result in changes in the combustion phase, reducing engine efficiency and increasing fuel consumption and emissions. However, the efficiency loss can be limited by estimating the combustion phase and adapting the spark timing, which could be implemented favorably using a closed-loop control approach. In this paper, we evaluate the efficiency loss resulting from varying gas compositions and the benefits of using a closed-loop controller to adapt the spark timing to retain the nominal combustion phase.

This study explores the potential benefits of combining a wave-shaped piston geometry with post injection strategy in diesel engines. The wave piston design features evenly spaced protrusions around the piston bowl, which improve fuel-air mixing and combustion efficiency. The 'waves' direct the flames towards the bowl center, recirculating them and utilizing the momentum in the flame jets for more complete combustion. Post injection strategy, which involves a short injection after the main injection, is commonly used to reduce emissions and improve fuel efficiency. By combining post injections with the wave piston design, additional fuel injection can increase the momentum utilized by the flame jets, potentially further improving combustion efficiency. To understand the effects and potential of the wave piston design with post injection strategy, a single-cylinder heavy-duty compression-ignition optical engine with a quartz piston is used.

The paper presents novel studies on the impact of different ignition control parameters on combustion stability and spark plug wear. First, experimental results from a 32.4-liter biogas fueled large bore single cylinder spark ignition engine are discussed. Two different ignition systems were considered in the experiment: a DC inductive and an AC capacitive. The spark plugs used in the experiment were of dual-iridium standard J-gap design of different electrode gaps. Test results show the importance of different degrees of freedom to control a spark. A robust ignition is found to be achieved by using a very short spark duration, which in turn reduces total energy discharge at the gap. Further observations reveal that once a stable and self-propagating flame kernel is developed, it becomes independent of the spark energy further added to the gap. Finally, results from the spark plug wear tests using a pressurized rig chamber are discussed.

The novel wave-shaped bowl piston geometry design with protrusions has been proved in previous studies to enhance late-cycle mixing and therefore significantly reduce soot emissions and increase engine thermodynamic efficiency. The wave-shaped piston is characterized by the introduction of evenly spaced protrusions around the inner wall of the bowl, with a matching number with the number of injection holes, i.e., flames. The interactions between adjacent flames strongly affect the in-cylinder flow and the wave shape is designed to guide the near-wall flow. The flow re-circulation produces a radial mixing zone (RMZ) that extends towards the center of the piston bowl, where unused air is available for oxidation promotion. The waves enhance the flow re-circulation and thus increase the mixing intensity of the RMZ.

Increasingly stringent pollutant and CO2 emission standards require the car manufacturers to investigate innovative solutions to further improve the fuel economy and environmental impact of their fleets. Nowadays, NOx emissions standards are stringent for spark-ignition (SI) internal combustion engines (ICEs) and many techniques are investigated to limit these emissions. Among these, an extremely lean combustion has a large potential to simultaneously reduce the NOx raw emissions and the fuel consumption of SI ICEs. Engines with pre-chamber ignition system are promising solutions for realizing a high air-fuel ratio which is both ignitable and with an adequate combustion speed. In this work, the combustion characteristics of an active pre-chamber system are experimentally investigated using a single-cylinder research engine. The engine under exam is a large bore heavy-duty unit with an active pre-chamber fuelled with compressed natural gas.

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.

The effect of an annular, piston bowl-rim cavity on in-cylinder and engine-out soot emissions is measured in a heavy-duty, optically accessible, single-cylinder diesel engine using in-cylinder soot diagnostics and exhaust smoke emission measurements. The baseline piston configuration consists of a right-cylindrical bowl, while the cavity-piston configuration features an additional annular cavity that is located below the piston bowl-rim and connected to the main-combustion chamber through a thin annular passage, accounting for a 3% increase in the clearance volume, resulting in a reduction in geometric compression ratio (CR) from 11.22 to 10.91. Experiments using the cavity-piston configuration showed a significant reduction of engine-out smoke ranging from 20-60% over a range of engine loads.

High-pressure internal combustion engines promise high efficiency, but a proper injection strategy to minimize heat losses and pollutant emissions remain a challenge. Previous studies have concluded that two injectors, placed at the piston bowl's rim, simultaneously improve the mixing and reduce the heat losses. The two-injector configuration further improves air utilization while keeping hot zones away from the cylinder walls. This study investigates how the two-injector concept delivers even higher efficiency by providing additional control of spray -and injection angles. Three-dimensional Reynolds-averaged Navier-Stokes simulations examined several umbrella angles, spray-to-spray angles, and injection orientations by comparing the two-injector cases with a reference one-injector case. The study focused on heat transfer reduction, where the two-injector approach reduces the heat transfer losses by up to 14.3 % compared to the reference case.

The constrained indicated efficiency optimization of the set-point reference for in-cycle closed-loop combustion regulators is investigated in this article. Closed-loop combustion control is able to reduce the stochastic cyclic variations of the combustion by the adjustment of multiple-injections, a pilot and main injection in this work. The set-point is determined by the demand on engine load, burned pilot mass reference and combustion timing. Two strategies were investigated, the regulation of the start of combustion (SOC) and the center of combustion (CA50). The novel approach taken in this investigation consists of including the effect of the controlled variables on the combustion dispersion, instead of using mean-value models, and solve the stochastic optimization problem. A stochastic heat release model is developed for simulation and calibrated with extensive data from a Scania D13 six-cylinder engine. A Monte Carlo approach is taken for the simulations.

Heavy-duty vehicles face increasing demands of emission regulations. Reduced carbon-dioxide (CO2) emission targets motivate decreased fuel consumption for fossil fuel engines. Increased engine efficiency contributes to lower fuel consumption and can be achieved by lower heat transfer, friction and exhaust losses. The double compression expansion engine (DCEE) concept achieves higher efficiency, as it utilizes a split-cycle approach to increase the in-cylinder pressure and recover the normally wasted exhaust energy. However, the DCEE concept suffers heat losses from the high-pressure approach. This study utilizes up to three injectors to reduce the wall-gas temperature gradient rendering lower convective heat losses. The injector configuration consists of a standard central injector and two side-injectors placed at the rim of the bowl. An increased distance from side-injector to the wall delivered lower heat losses by centralizing hot gases in the combustion chamber.

Methanol is not a fuel typically used in compression ignition engines due to the high resistance to auto-ignition. However, conventional diesel combustion and PPC offer high engine efficiency along with low HC and CO emissions, albeit with the trade-off of increased NOx and PM emissions. This trade-off balance is mitigated in the case of methanol and other alcohol fuels, as they bring oxygen in the combustion chamber. Thus methanol compression ignition holds the potential for a clean and effective alternative fuel proposition. Most existing research on methanol is on SI engines and very little exists in the literature regarding methanol auto-ignition engine concepts. In this study, the spray characteristics of methanol inside the optically accessible cylinder of a DI-HD engine are investigated. The liquid penetration length at various injection timings is documented, ranging from typical PPC range down to conventional diesel combustion.

Pilot injections are normally used for the reduction of diesel engine emissions and combustion noise. Nonetheless, with a penalty on the indicated thermal efficiency. The cost is reduced by the minimization of the pilot mass, which on its counterpart increases the risk of pilot misfire. Pilot misfire can have a higher penalty on the indicated efficiency if it is not compensated adequately. This paper investigates how in-cycle closed-loop combustion control techniques can reduce the effects of pilot misfire events. By closed-loop combustion control, pilot misfire can be detected and counteracted in-cycle. Two injection strategies are investigated. The first is the control of the main injection, the second includes an additional second pilot injection. Based on the in-cycle misfire diagnose, two architectures are investigated. The first uses a cycle-to-cycle controller to set the main injection under each scenario.

Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on stationary engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of a pre-chamber combustion configuration in a stationary heavy-duty engine for power generation, operating at different loads, air-to-fuel ratios and spark timings.

This study investigates particulate matter (PM) and regulated emissions from renewable rapeseed oil methyl ester (RME) biodiesel in pure and blended forms and contrasts that to conventional diesel fuel. Environmental and health concerns are the major motivation for combustion engines research, especially finding sustainable alternatives to fossil fuels and reducing diesel PM emissions. Fatty acid methyl esters (FAME), including RME, are renewable fuels commonly used from low level blends with diesel to full substitution. They strongly reduce the net carbon dioxide emissions. It is largely unknown how the emissions and characteristics of PM get altered by the combined effect of adding biodiesel to diesel and implementing modern engine concepts that reduce nitrogen oxides (NOx) emissions by exhaust gas recirculation (EGR).

In this paper, computation fluid dynamics (CFD) simulations are performed to describe the effect of in-cylinder flow structures on the formation and oxidation of soot in a swirl-supported light-duty diesel engine. The focus of the paper is on the effect of swirl motion and injection pressure on late cycle soot oxidation. The structure of the flow at different swirl numbers is studied to investigate the effect of varying swirl number on the coherent flow structures. These coherent flow structures are studied to understand the mechanism that leads to efficient soot oxidation in late cycle. Effect of varying injection pressure at different swirl numbers and the interaction between spray and swirl motions are discussed. The complexity of diesel combustion, especially when soot and other emissions are of interest, requires using a detailed chemical mechanism to have a correct estimation of temperature and species distribution.

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.

Methanol is a genuine candidate on the alternative fuel market for internal combustion engines, especially within the heavy-duty transportation sector. Partially premixed combustion (PPC) engine concept, known for its high efficiency and low emission rates, can be promoted further with methanol fuel due to its unique thermo-physical properties. The low stoichiometric air to fuel ratio allows to utilize late injection timings, which reduces the wall-wetting effects, and thus can lead to less unburned hydrocarbons. Moreover, combustion of methanol as an alcohol fuel, is free from soot emissions, which allows to extend the operation range of the engine. However, due to the high latent heat of vaporization, the ignition event requires a high inlet temperature to achieve ignition event. In this paper LES simulations together with experimental measurements on an heavy-duty optical engine are used to study methanol PPC engine.

Heat losses are known to decrease the efficiency of CI engines largely. Here, multiple injectors have been suggested to shrink these losses through reduction of spray wall impingement. Studies on multiple injectors have proven the concept’s heat transfer reduction but also highlighted the difficulty of using a standard piston bowl. This study proposes a two-injector concept combined with a flat bowl to reduce heat losses further. To change the spray pattern, the two injectors are injecting in a swirling motion while placed at the rim of the bowl. Four injection timings have been investigated using Reynolds-Averaged Navier-Stokes simulations. This computational method quantified the amount of heat loss reduction possible. A conventional single injector concept is compared to two injector concepts with a standard and flat bowl. A Double Compression Expansion Engine (DCEE) concept, based on a modified Volvo D13 single-cylinder engine, was the base for all simulations.