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In the last two decades engine research has been mainly focused on reducing pollutant emissions. This fact together with growing awareness about the impacts of climate change are leading to an increase in the importance of thermal efficiency over other criteria in the design of internal combustion engines (ICE). In this framework, the heat transfer to the combustion chamber walls can be considered as one of the main sources of indicated efficiency diminution. In particular, in modern direct-injection diesel engines, the radiation emission from soot particles can constitute a significant component of the efficiency losses. Thus, the main of objective of the current research was to evaluate the amount of energy lost to soot radiation relative to the input fuel chemical energy during the combustion event under several representative engine loads and speeds. Moreover, the current research characterized the impact of different engine operating conditions on radiation heat transfer.

With ever-demanding emission legislations in Compression Ignition (CI) engines, new premixed combustion strategies have been developed in recent years seeking both, emissions and performance improvements. Since it has been shown that in-cylinder air flow affects the combustion process, and hence the overall engine performance, the study of swirling structures and its interaction with fuel injection are of great interest. In this regard, possible Turbulent Kinetic Energy (TKE) distribution changes after fuel injection may be a key parameter for achieving performance improvements by reducing in-cylinder heat transfer. Consequently, this paper aims to gain an insight into spray-swirl interaction through the analysis of in-cylinder velocity fields measured by Particle Image Velocimetry (PIV) when PCCI conditions are proposed. Experiments are carried out in a single cylinder optical Diesel engine with bowl-in-piston geometry.

This work investigates the particulates size distribution of reactivity controlled compression ignition combustion, a dual-fuel concept which combines the port fuel injection of low-reactive/gasoline-like fuels with direct injection of highly reactive/diesel-like fuels. The particulates size distributions from 5-250 nm were measured using a scanning mobility particle sizer at six engine speeds, from 950 to 2200 rpm, and 25% engine load. The same procedure was followed for conventional diesel combustion. The study was performed in a single-cylinder engine derived from a stock medium-duty multi-cylinder diesel engine of 15.3:1 compression ratio. The combustion strategy proposed during the tests campaign was limited to accomplish both mechanical and emissions constraints. The results confirms that reactivity controlled compression ignition promotes ultra-low levels of nitrogen oxides and smoke emissions in the points tested.

Growing awareness about CO2 emissions and their environmental implications are leading to an increase in the importance of thermal efficiency as criteria to design internal combustion engines (ICE). Heat transfer to the combustion chamber walls contributes to a decrease in the indicated efficiency. A strategy explored in this study to mitigate this efficiency loss is to promote low swirl conditions in the combustion chamber by using low swirl ratios. A decrease in swirl ratio leads to a reduction in heat transfer, but unfortunately, it can also lead to worsening of combustion development and a decrease in the gross indicated efficiency. Moreover, pumping work plays also an important role due to the effect of reduced intake restriction to generate the swirl motion. Current research evaluates the effect of a dedicated injection strategy to enhance combustion process when low swirl is used.

Most of the new Diesel combustion concepts are mainly based on reducing local combustion temperatures and enhancing the fuel/air mixing with the aim of simultaneously reducing soot and NOx emissions. In this framework, Premixed Charge Compression Ignition (PCCI) has revealed as one of the best options to combine both low emissions and good combustion controllability. During last years, PCCI strategy has been widely explored using high EGR levels and different early or late injection timings to extend the ignition delay. Recently, the use of lower cetane fuels is under investigation. Despite the great quantity of research work performed, there are still some aspects related to PCCI combustion that are not completely well known. In this paper an experimental and numerical study is carried out focused on understanding the mixing and auto-ignition processes in PCCI combustion conditions using Diesel and Gasoline fuels.

A comprehensive study is carried out in order to better understand combustion behavior in a direct injection Diesel engine working under multiple injection strategies, in particular when using post-injections. The aim of the study is to provide criteria to more easily define optimized injection strategies. During the study two main phenomena have been observed and characterized: an acceleration of the final stage of combustion and an apparent disconnection between the combustions of the two pulses (“split flame”). Thanks to the combustion acceleration phenomenon, if the post-injection is placed near enough the main injection, the end of combustion can take place even earlier compared to the case with a single main injection. In such conditions NOx emissions increase (most likely due to a higher temperature level during the last stage of combustion), but soot and specific fuel consumption decrease (due to a faster last phase of combustion).

Engine-out soot emissions are the result of a complex balance between in-cylinder soot formation and oxidation. Soot is formed in the diffusion flame, just after the lift-off length (LOL). Size and mass of soot particles increase through the diffusion flame and finally they are partially oxidized at the flame front. Therefore, engine-out soot emissions depend on the amount of soot formed and oxidized inside the combustion chamber. There is a considerable amount of work in the literature on characterization of soot formation. However, there is a clear lack of published research related to the characterization of soot oxidation. Thus, the main objective of the current research is to provide more knowledge and insight into the soot oxidation processes. For this purpose, a combination of theoretical and experimental tools were used. In particular, in-cylinder optical thickness (KL) was quantified with an optoelectronic sensor that uses two-color pyrometry.

Regulated emissions and fuel consumption are the main constraints affecting internal combustion engine (ICE) design. Over the years, many techniques have been used with the aim of meeting these limitations. In particular, exhaust gas recirculation (EGR) has proved to be an invaluable solution to reduce NOx emissions in Diesel engines, becoming a widely used technique in production engines. However, its application has a direct effect on fuel consumption due to both the changes in the in-cylinder processes, affecting indicated efficiency, and also on the air management. An analysis, based on the engine Global Energy Balance, is presented to thoroughly assess the behavior of a HSDI Diesel engine under variable EGR conditions at different operating points. The tests have been carried out keeping constant the conditions at the IVC and the combustion centering.

In-cylinder emission control strategies, such as modifications of injection pressure and injection timing, have been used by researchers in order to reduce exhaust emissions and to comply with the legislation standards. Since some years ago post-injections have been studied and are well known as being efficient for soot emissions reduction. Although is well known that diesel gaseous and particle mass emissions have been reduced progressively over the last twenty years in response to the restrictive emission legislation and due to the application of new technologies The aim of this work is to help develop and understand the effect of the post-injection on diesel exhaust particle size distributions. The approach is to use a modern, well instrumented research engine equipped with a flexible high pressure fuel injection system. The results of this work are available to help provide guidelines for strategies to achieve reductions of the particle size distributions in diesel engines.

Ever decreasing permitted emission levels and the necessity of more efficient engines demand a better understanding of in-cylinder phenomena. In swirl-supported compression ignition (CI) engines, mean in-cylinder flow structures formed during the intake stroke deeply influence mixture preparation prior to combustion, heat transfer and pollutant oxidation all of which could potentially improve engine performance. Therefore, the ability to characterize these mean flow structures is relevant for achieving performance improvements. CI mean flow structure is mainly described by a precessing vortex. The location of the vortex center is key for the characterization of the flow structure. Consequently, this work aims at evaluating algorithms that allow for the location of the vortex center both, in ensemble-averaged velocity fields and in instantaneous velocity fields.

The dual-fuel combustion mode known as reactivity controlled compression ignition (RCCI) allows an effective control of the combustion process by means of modulating the in-cylinder fuel reactivity depending on the engine operating conditions. This strategy has been found to be able to avoid the NOx-soot trade-off appearing during conventional diesel combustion (CDC), with diesel-like or better thermal efficiency in a great part of the engine map. The role of the low reactivity fuel properties and engine settings over RCCI combustion has been widely investigated in literature, concluding that the direct-injected fuel injection timing is a key parameter for controlling the in-cylinder fuel stratification. From this, it can be inferred that the physical and chemical characteristics of the direct-injected fuel should have also an important role on the RCCI combustion process.

Pure biodiesel is non-toxic, biodegradable and greenhouse gas neutral alternative fuel with potential successful future but reduced quantitative information is available about the impact of biodiesel on engine durability and long period usage effects. In this study, a commercial light duty Diesel engine installed on an engine test bench has been operated fuelled with pure biodiesel (B100 referred to the EN-14214 standard) during a period test of 300 hours in order to analyze engine performance and components behavior. A engine characterization has been completed using conventional diesel fuel (EN 590). Then, following a specific defined operation cycle and fuelled with pure biodiesel, a study over different engine components such as: engine oil, fuel filters, Diesel Particulate Filter (DPF), so on, has been done in order to obtain possible negative effects and modifications required over maintenance policies applied to them.

Several new combustion concepts have been developed during last decade with the aim of reducing pollutant emissions. Specifically, these strategies allow a simultaneous reduction of NOx and soot emissions by reducing the local combustion temperatures, enhancing the fuel/air mixing (PCCI, HCCI…). In spite of their benefits, these concepts present difficulties controlling the appropriate combustion phasing as well as high knocking levels and therefore, their operating range is reduced to low-medium loads. In this work gasoline is considered as a fuel in order to improve combustion strategies based on fully or partially premixed combustion in CI engines. Its use provides more flexibility to achieve lean and low combustion temperature, however the concept has demonstrated difficulty under light load conditions using gasoline with ON up to 95.

Compared to the gasoline engine, the diesel engine has the advantage of being more efficient and hence achieving a reduction of CO₂ levels. Unfortunately, particulate matter (PM) and nitrogen oxides (NOx) emissions from diesel engines are high. To overcome these drawbacks, several new combustion concepts have been developed, including the PCCI (Premixed Charge Compression Ignition) combustion mode. This strategy allows a simultaneous reduction of NOx and soot emissions through the reduction of local combustion temperatures and the enhancement of the fuel/air mixing. In spite of PCCI benefits, the concept is characterized by its high combustion noise levels. Currently, a promising way to improve the PCCI disadvantages is being investigated. It is related with the use of low cetane fuels such as gasoline and diesel-gasoline blends.

Engine Combustion Network promotes fundamental investigations on a number of different spray configurations with the goal of providing experimental results under highly controlled conditions for CFD validation. Most of the available experiments up to now have been obtained in spray vessels, which miss some of the interactions governing spray evolution in the combustion chamber of an engine, such as the jet wall interaction and the transient conditions in the combustion chamber. The main aim of the present research is to compare the results obtained with a three-hole, 90 μm injector, known as ECN’s Spray B, in these constant-volume vessels and more recent Heavy-Duty engines with those obtained in a Light Duty Single Cylinder Optical Engine, under inert and reactive conditions, using n-dodecane. In-cylinder conditions during the injection were estimated by means of a 1-D and 0-D model simulation, accounting for heat transfer and in-cylinder mass evolution.

Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at low, mid, and high loads. By coupling the KIVA-3V code with the enhanced genetic algorithm (GA), a total of 14 parameters including the piston bowl geometric parameters and the injection parameters were optimized with the objective of meeting Euro VI regulations while improving the fuel efficiency. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized and integrated at various loads. Furthermore, the effects of the key geometric parameters were investigated in terms of organizing the in-cylinder flow, influencing the energy distribution, and affecting the emissions. The results indicate that the behavior of the DMDF combustion mode is further enhanced in the aspects of improving the fuel economy and controlling the emissions after the bowl geometry optimization.

Electrification and hybridization of powerplants in the transportation sector is one of the most important changes in the last few decades. Lithium-ion batteries are the main energy storage systems, but despite the maturity of this technology, it has certain constrains compared to traditional internal combustion engines in the day-to-day usage. As the operating conditions of the batteries are pushed to the limits to overcome certain disadvantages relative to other conventional systems like charge and discharge times or vehicle driving range, new concerns and safety limitations must be considered. High power rates and cooling deficiencies can produce excessive operating temperatures within the cells, leading to problems with degradation or even unchain chemical reactions that can end in thermal runaway, one of the most worrying failure modes attaining electric platforms nowadays.

In the challenge to reduce CO2, NOx and PM emissions, the application of natural gas or biogas in engines is a viable approach. In heavy duty and marine, either a conventional dual fuel (CDF), or a reactivity-controlled compression ignition (RCCI) approach is feasible on existing diesel engines. In both technologies a pilot diesel injection is used to ignite the premixed natural gas. However, the influence of injection-timing and -pressure on the start of combustion timing (SOC) is opposite between both modes. For a single operating point these relations can be explained by a detailed CFD simulation, but an intuitive overall explanation is lacking. This makes it difficult to incorporate both modes into one engine application, using a single controller. In an experimental campaign by the authors, on a medium speed engine, the lowest emissions were found to be very close to the SOC corresponding to the transition from RCCI to CDF.

Reactivity controlled compression ignition (RCCI) combustion has demonstrated to be able to avoid the NOx-soot trade-off appearing during conventional diesel combustion (CDC), with similar or better thermal efficiency than CDC under a wide variety of engine platforms. However, a major challenge of this concept comes from the high hydrocarbon (HC) and carbon monoxide (CO) emission levels, which are orders of magnitude higher than CDC and similar to those of port fuel injected (PFI) gasoline engines. The higher HC and CO emissions combined with the lower exhaust temperatures during RCCI operation present a challenge for current exhaust aftertreatment technologies. RCCI has been successfully implemented on different compression ignition engine platforms with only minor modifications on the combustion system to include a PFI for feeding the engine with the low reactivity fuel.

With demanding emissions legislations and the need for higher efficiency, new technologies for compression ignition engines are in development. One of them relies on reducing the heat losses of the engine during the combustion process as well as to devise injection strategies that reduce soot formation. Therefore, it is necessary a better comprehension about the turbulent kinetic energy (TKE) distribution inside the cylinder and how it is affected by the interaction between air flow motion and fuel spray. Furthermore, new diesel engines are characterized by massive decrease of NOx emissions. Therefore, considering the well-known NOx-soot trade-off, it is necessary a better comprehension and overall quantification of soot formation and how the different injection strategies can impact it.