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Feed-forward low-throughput models have been developed to predict MFB50 and to control SOI in order to achieve a specific MFB50 target for diesel engines. The models have been assessed on a GMPT-E Euro 5 diesel engine, installed at the dynamic test bench at ICEAL-PT (Internal Combustion Engine Advanced Laboratory at the Politecnico di Torino) and applied to both steady state and transient engine operating conditions. MFB50 indicates the crank angle at which 50% of the fuel mass fraction has burned, and is currently used extensively in control algorithms to optimize combustion phasing in diesel engines in real-time. MFB50 is generally used in closed-loop combustion control applications, where it is calculated by the engine control unit, cycle-by-cycle and cylinder by-cylinder, on the basis of the measured in-cylinder pressure trace, and is adjusted in order to reduce the fuel consumption, combustion noise and engine-out emissions.

In this work, an ozone/air/gasoline mixture has been used as an alternative strategy to achieve a stable combustion in a spark ignition (SI) single cylinder PFI research engine. The air intake manifold has been modified to include four cells to produce ozone with different concentrations. In the research engine, various operating parameters have been monitored such as the in-cylinder pressure, temperature and composition of the exhaust gases, pressure and temperature of the mixture in the intake manifold, engine power and torque and specific fuel consumption. Experimental tests have been carried out under stoichiometric mixture conditions to observe the influence of ozone addition on the combustion process. The results show an advance and an increase of the in-cylinder pressure compared to the reference test-case, where a gasoline/air mixture is used. It is worth noting that, especially under stoichiometric condition, ozone concentration induces auto-ignition and knock.

A quasi-dimensional multizone combustion model, that was previously developed by the authors, has been refined and applied for the analysis of combustion and emission formation in a EURO V diesel engine equipped with a piezo indirect-acting injection system. The model is based on the integration of the predictive non-stationary variable-profile 1D spray model recently presented by Musculus and Kattke, with a diagnostic multizone thermodynamic model specifically developed by the authors. The multizone approach has been developed starting from the Dec conceptual scheme, and is based on the identification of several homogeneous zones in the combustion chamber, to which mass and energy conservation laws have been applied: an unburned gas zone, made up of air, EGR (Exhaust Gas Recirculation) and residual gas, several fuel/unburned gas mixture zones, premixed combustion burned gas zones and diffusive combustion burned gas zones.

In the perspective of a reduction of emissions and a rapid decarbonisation, especially for compression ignition engines, hydrogen plays a decisive role. The dual fuel technology is perfectly suited to the use of hydrogen, a fuel characterized by great energy potential. In fact, replacing, at the same energy content, the fossil fuel with a totally carbon free one, a significant reduction of the greenhouse gases, like carbon dioxide and total hydrocarbon, as well as of the particulate matter can be obtained. The dual fuel with indirect injection of gaseous fuel in the intake manifold, involves the problem of hydrogen autoignition. In order to avoid this difficulty, the optimal conditions for the injection of the incoming mixture into the cylinder were experimentally investigated. All combustion processes are carried out on a research engine with optical access. The engine speed has is set at 1500 rpm, while the EGR valve is deactivated.

An innovative quasi-dimensional multizone combustion model for the spray formation, combustion and emission formation analysis in DI diesel engines was assessed and applied to an optical single cylinder engine. The model, which has been recently presented by the authors, integrates a predictive non stationary 1D spray model developed by the Sandia National Laboratory, with a diagnostic multizone thermodynamic model. The 1D spray model is capable of predicting the equivalence ratio of the fuel during the mixing process, as well as the spray penetration. The multizone approach is based on the application of the mass and energy conservation laws to several homogeneous zones identified in the combustion chamber. A specific submodel is also implemented to simulate the dilution of the burned gases. Soot formation is modeled by an expression which derives from Kitamura et al.'s results, in which an explicit dependence on the local equivalence ratio is considered.

Although in the latest years the use of compression ignition engines has been a thread of discussion in the automotive field, it is possible to affirm that it still will be a fundamental producer of mechanical power in other sectors, such as naval and off-road applications. However, the necessity of reducing emissions requires to keep on studying new solutions for this kind of engine. Dual fuel combustion concept with methane has demonstrated to be effective in preserving the performance of the original engine and reducing soot, but issues related to the low flame speed forced researcher to find an alternative fuel at low impact of CO2. Hydrogen, thanks to its chemical and physical properties, can be a perfect candidate to ensure a good level of combustion efficiency; however, this is possible only with a proper management of the in-cylinder mixture ignition by means of a pilot injection, preventing uncontrolled autoignition events as well.

This paper reports experiments on a single-cylinder direct-injection compression ignition engine operating in premixed charge compression ignition (PCCI) combustion mode. The engine was fuelled with pure rapeseed methyl ester (RME) and bio-ethanol. RME was injected in the combustion chamber by common rail (CR) injection system at 800 bar and bio-ethanol in the intake manifold by commercial port fuel injection system at 3.5 bar. The effects of different percentage of bio-ethanol were studied by means of both the in-cylinder heat release analysis and the high-speed UV-visible chemiluminescence visualization. The pollutant formation and exhaust emissions of the engine operating in dual fuel mode were evaluated. The increase of the bio-ethanol content improved the brake thermal efficiency slightly even if the brake fuel consumption increased. However, the choice to inject two biofuels decreases both the smoke opacity and NOx concentration.

Interest on the issue of diesel injector nozzle deposits is rising in the last years due to its effects on engine performance. The alteration of nozzles geometry can cause a difference in fuel mass flow and influence smoke emission. Investigation on the effects of nozzle coking in a diesel injector has been the topic of this paper. The experiments have been carried out in a single cylinder optical engine operating in premixed mode. The head of a Euro 5 production engine has been mounted on an elongated cylinder and the production CR injection system has been used. A sapphire window has been set in the piston head in order to have visible access to phenomena occurring in the combustion chamber. Three injectors with decreasing flow number (FN) have been tested. Engine has been fed with commercial diesel fuel. High spatial and temporal resolution camera has been used for the acquisition of in-cylinder injection and combustion images.

Methane supply in diesel engines operating in dual fuel mode has demonstrated to be effective for the reduction of particulate matter and nitric oxides emissions from this type of engine. In particular, methane is injected into the intake manifold to form a premixed charge with air, while a reduced amount of diesel oil is still directly injected to ignite the mixture inside the cylinder. As a matter of fact, the liquid fuel burns following the usual diffusive combustion, so activating the gaseous fuel oxidation in a premixed flame. Clearly, the whole combustion process appears to be more complex to be described in a CFD simulation, mainly because it is not always possible to select in the 3-dimensional codes a different combustion model for each fuel and, also, because other issues arise from the interaction of the two fuels.

In this paper we report how optical techniques were applied in the cylinder of an optically accessible engine equipped with latest-generation EURO V diesel engine head. The injection strategy with high percentage of EGR, characteristic of real engine operating point, was adopted. In particular, the combustion behavior at 1500 rpm\2 bar BMEP was investigated. Alternative diesel fuels were used. In particular, rapeseed methyl ester (RME) and gas to liquid (GTL) were selected as representative of 1st and 2nd generation alternative diesel fuel, respectively. Combustion analysis was carried out in the engine combustion chamber by means of visible digital imaging. These measurements helped to analyze the chemical and physical events occurring during the mixture preparation and the combustion development. Ultraviolet (UV) digital imaging was also performed and the presence of characteristic radical, like OH, in the various phases of combustion was detected as well.

Pressure-based and model-based techniques for the control of MFB50 (crank angle at which 50% of the fuel mass fraction has burned) have been developed, assessed and tested by means of rapid prototyping (RP) on a FPT F1C 3.0L Euro VI diesel engine. The pressure-based technique requires the utilization of a pressure transducer for each cylinder. The transducers are used to perform the instantaneous measurement of the in-cylinder pressure, in order to derive its corresponding burned mass fraction and the actual value of MFB50. It essentially consists of a closed-loop approach, which is based on a cycle-by-cycle and cylinder-to-cylinder correction of the start of injection of the main pulse (SOImain), in order to achieve the desired target of MFB50 for each cylinder.

Natural gas is a promising alternative fuel for internal combustion engine application due to its low carbon content and high knock resistance. Performance of natural gas engines is further improved if direct injection, high turbocharger boost level, and variable valve actuation (VVA) are adopted. Also, relevant efficiency benefits can be obtained through downsizing. However, mixture quality resulting from direct gas injection has proven to be problematic. This work aims at developing a mono-fuel small-displacement turbocharged compressed natural gas engine with side-mounted direct injector and advanced VVA system. An injector configuration was designed in order to enhance the overall engine tumble and thus overcome low penetration.

Increasing demands on emissions reduction and efficiency encouraged a progressive introduction of cleaner combustion concepts. "Advanced" diesel combustions offer a high potential for simultaneous reduction of both NOx and soot within the engine through high inlet charge dilution and mixture homogenization. However, the potential benefits of these combustions in terms of emissions are counterbalanced by their high sensitivity to in-cylinder thermodynamic conditions. This sensitivity makes the engines require closed loop combustion control with real-time information about combustion quality. The parameter widely considered as the most important for the evaluation of the combustion quality in internal combustion engines is the cylinder pressure. However, this kind of measure involves an intrusive approach to the cylinder, expensive sensors and a special mounting process.

An innovative approach to the study of combustion and emission formation in modern diesel engines has been applied to a EURO V diesel engine equipped with an indirect-acting piezo injection system. The model is based on the joint use of a predictive non-stationary 1D spray model, which has recently been presented by Musculus and Kattke, and a diagnostic multizone thermodynamic model developed by the authors. The combustion chamber content has been split into homogeneous zones, to which mass and energy conservation laws have been applied: an unburned gas zone, made up of air, EGR and residual gas, several fuel/unburned gas mixture zones, premixed combustion burned gas zones and diffusive combustion burned gas zones. The 1D spray model enables the mixing process dynamics of the different fuel parcels with the unburned gas to be estimated for each injection pulse; therefore, the equivalent ratio time-history of each mixture zone can be estimated.

This work reports on the application of spectroscopic measurements coupled with data processing techniques in order to study, in terms of spectral emissions, the dynamic of the HCCI (Homogeneous charge compression ignition) combustion that occurs inside the combustion chamber of an optically accessible direct injection Diesel engine. A pre-processing of the recorded spectra is required for a correct analysis. The procedure of pre-processing consists of two main steps, that is: noise filtering with a technique based on the POD (Proper Orthogonal Decomposition); estimate and subtraction of the baseline. The analysis of the dynamics of the recorded spectra was carried out by the estimates of the synchronous and asynchronous 2D correlation spectra.

The management of multiple injections in compression ignition (CI) engines is one of the most common ways to increase engine performance by avoiding hardware modifications and after-treatment systems. Great attention is given to the profile of the injection rate since it controls the fuel delivery in the cylinder. The Injection Rate Shaping (IRS) is a technique that aims to manage the quantity of injected fuel during the injection process via a proper definition of the injection timing (injection duration and dwell time). In particular, it consists in closer and centered injection events and in a split main injection with a very small dwell time. From the experimental point of view, the performance of an IRS strategy has been studied in an optical CI engine. In particular, liquid and vapor phases of the injected fuel have been acquired via visible and infrared imaging, respectively. Injection parameters, like penetration and cone angle have been determined and analyzed.

Homogeneous Charge Compression Ignition (HCCI) combustion was applied to a transparent diesel engine equipped with high pressure Common Rail (CR) injection system. By means of CR system the quantity of fuel was split into five injections per cycle. Combined measurements, based on digital imaging and spectroscopic techniques, were applied to follow the evolution of HCCI combustion process with high temporal and spatial resolution. Digital imaging allowed to analyse injection and combustion phases. Broadband ultraviolet - visible extinction spectroscopy (BUVES) and flame emission measurements were carried out to evaluate the presence of radicals and species such as HCO, OH, CH, and CO. In particular, BUVES measurements were performed to follow fuel oxidation, and pollutant formation and oxidation. During injection and cool combustion, bands of aromatic compounds and alkyl peroxides, indicating fuel decomposition, and hydrogen peroxides were detected.

Nowadays HCCI combustion process is revealing the most useful technique for reducing pollutant emission from internal combustion engines. In the present paper, HCCI combustion was realized by means of single late injection at high pressure and heavy EGR, up to 50%. A transparent Direct Injection (DI) diesel engine equipped with high pressure Common Rail (CR) injection system was used. The engine was fed with commercial diesel fuel and ran in continuous mode. Digital imaging and spectroscopic techniques, with high temporal and spatial resolution, were applied to study the low temperature combustion process. Injection and combustion phases were analysed by digital imaging. Mixing process, autoignition and pollutants formation were investigated by Broadband Ultraviolet - Visible Extinction Spectroscopy (BUVES) and flame emission measurements. Radicals and species such as OH, CH and CO were detected in the combustion chamber.

With the aim of decarbonizing the vehicles fleet, the use of hydrogen is promising solution. Hydrogen is an energy carrier, carbon-free, with high calorific value and with no CO2 and HC emissions burning in ICE. Hydrogen use in spark ignition engines has already been extensively investigated and optimized. On the other hand, its use in compression ignition engines has been little developed and, therefore, there is a lack of information regarding the combustion in ultra-lean conditions, typical of diesel engines. Several applications employ dual fuel combustion for the easy management of the PFI injection system to be applied in addition to the DI Common Rail system. However, this mode suffers from several problems regarding the management of the maximum flow rate of hydrogen into the intake. In particular, to avoid throwing hydrogen into the exhaust, injection must be started after the valve crossing.

The application of an alternative fuel such as hydrogen to internal combustion engines is proving to be an effective and flexible solution for reducing fuel consumption and polluting emissions from engines. An easy to use and immediate application solution is the dual fuel (DF) technology. It has the potential to offer significant improvements in carbon dioxide emissions from light compression ignition engines. The dual fuel concept (natural gas / diesel or hydrogen / diesel) represents a possible solution to reduce emissions from diesel engines by using low-carbon or carbon-free gaseous fuels as an alternative fuel. Moreover, DF combustion is a possible retrofit solution to current diesel engines by installing a PFI injector in the intake manifold while diesel is injected directly into the cylinder to ignite the premixed mixture. In the present study, dual fuel operation has been investigated in a single cylinder research engine.