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Over the last years, automotive industries drove a great amount of research in the field of advanced combustion techniques minimizing carbon dioxide emissions. The so-called Low-Temperature Combustions (LTC), characterized by the self-ignition of highly premixed air-fuel mixtures, represent a promising solution to achieving high efficiency and ultralow emissions of nitrogen oxides (NOx) and particulate matter. Among these, gasoline Partially Premixed Combustion (PPC), obtained through the high-pressure direct injections of gasoline, showed a good potential for the simultaneous reduction of pollutants and emissions in compression ignited engines. However, when multiple injections per cycle are performed (with hydraulic-assisted needle opening), combustion stability might be compromised by the wave effects in the hydraulic system, which produce incoherence between the requested and injected fuel. This work presents a model-based pressure waves reconstruction strategy, based on a control-oriented model of the high-pressure common rail injection system fueled with gasoline. To determine the hydraulic system's behavior during the injection process, a specifically designed flushing bench with a high-frequency acquisition system has been developed. Experimental activities have been carried out to highlight fuel pressure fluctuations with single and double injection patterns. Through the analysis of the acquired data, the key parameters (characteristic of the system) have been identified and the accuracy of pressure waves reconstruction has been evaluated, always returning errors lower than 2% between measured and estimated instantaneous pressures. Different fuel types, injectors, and rail positions have been tested to highlight the robustness of the approach. Based on the instantaneous pressure trace estimated with the control-oriented model, a fuel quantity Fluctuation Correction Strategy (FQC), implementable on a standard engine Electronic Control Unit (ECU), has been developed. The obtained results confirm the potential to reduce fuel quantity oscillations in multiple-injections systems.

Nowadays, progressive improvements of engine performance must be performed to reduce fuel consumption, which directly affects the amount of CO2 released in the atmosphere. For this purpose, considering modern technologies in the automotive scenario, Gasoline Compression Ignition (GCI) combustion might represent one promising solution, since it experiences high thermal efficiency of Compression Ignited (CI) engines and pollutant emission mitigation. This paper shows the first step of a project aimed at reproducing the combustion behavior of a Diesel engine running with GCI combustion by means of CFD simulations. In particular, this work presents a methodology used to reconstruct the mixing process inside the cylinder before the combustion event, since those engines are dramatically sensitive to the global and local mixture quality. Firstly, a reverse-engineering procedure aimed at generating the CAD model of the engine was performed. Afterwards, the discharge coefficients of the intake and exhaust valves through specifically designed 3D CFD simulations were determined, which was necessary due to the customized intake/exhaust line. Eventually, to reasonably reconstruct the in-cylinder state, the Rate of Heat Release (RoHR) curve, calculated from the analysis of the in-cylinder pressure signal running the engine in GCI mode, was imposed in GT-Power by means of a combination of Wiebe functions with the purpose of generating representative trends of pressure, temperature, and mass flow to properly define the domains of the CFD model.

Compression ignited engines are still considered the most efficient and reliable technology currently available for power generation in automotive applications. In this scenario, the main obstacles to the use of conventional compression-ignited engines are the increasingly stringent emission regulations, which require significant increases in engine efficiency and severely limit both NOx and particulate matter production. As a matter of fact, the combustion process that occurs in conventional compression-ignited engines, mainly characterized by the auto-ignition of directly injected Diesel-like fuels, is a heterogeneous process usually not compatible with modern emission regulations. To overcome the mentioned critical issues, a large amount of research is being carried out to investigate the combined use of gasoline-like fuels and compression-ignited engines, which proved to be very promising to simultaneously achieve high efficiency and low emissions. One of the main critical issues related to the auto-ignition of gasoline-like fuels is the high sensitivity to the thermal conditions of the cylinder, which results in long ignition delays strongly variable with small cylinder temperature variations. This work proposes a testing methodology suitable to investigate how the residual gases trapped inside the combustion chamber affect cylinder thermal conditions and, consequently, the gasoline auto-ignition mechanisms. The testing methodology is based on a specifically designed injection control strategy that manages the cylinders independently: one cylinder is operated using a proper pattern of gasoline direct injections, while the others are operated only to vary the intake and exhaust conditions of the first cylinder, where gasoline compression ignition is studied. The testing methodology, applied to an engine installed in a test cell, proved to be effective to highlight the effect of the residual gases on gasoline auto-ignition.

Increasingly stringent pollutant emission limits and CO2 reduction policies are forcing the automotive industry toward cleaner and decarbonized mobility. The goal is to achieve carbon neutrality within 2050 and limit global warming to 2 °C (possibly 1.5 °C) with respect to pre-industrial levels as stated in both the European Green Deal and the Paris Agreement and further reiterated at the COP26. With the aim of simultaneously reducing both pollutants and CO2 emissions, a large amount of research is currently carried out on low-temperature highly efficient combustions (LTC). Among these advanced combustions, one of the most promising is Gasoline Compression Ignition (GCI), based on the spontaneous ignition of a gasoline-like fuel. Nevertheless, despite GCI proving to be effective in reducing both pollutants and CO2 emissions, GCI combustion controllability represents the main challenge that hinders the diffusion of this methodology for transportation. Several works in the literature demonstrated that to properly control GCI combustion, a multiple injections strategy is needed. The rise of pressure and temperature generated by the spontaneous ignition of small amounts of early-injected fuel reduces the ignition delay of the following main injection, responsible for the torque production of the engine. Since the combustion of the pre-injections is chemically driven, the ignition delay might be strongly affected by a slight variation in the engine control parameters and, consequently, lead to misfire or knocking. The goal of this work was to develop a control-oriented ignition delay model suitable to improve the GCI combustion stability through the proper management of the pilot injections. After a thorough analysis of the quantities affecting the ignition delay, this quantity was modeled as a function of both a thermodynamic and a chemical–physical index. The comparison between the measured and modeled ignition delay shows an accuracy compatible with the requirements for control purposes (the average root mean squared error between the measured and estimated start of combustion is close to 1.3 deg), over a wide range of operating conditions. As a result, the presented approach proved to be appropriate for the development of a model-based feed-forward contribution for a closed-loop combustion control strategy.

Compression-ignited engines are still considered the most efficient and reliable technology for automotive applications. However, current and future emission regulations, which severely limit the production of NOx, particulate matter and CO2, hinder the use of diesel-like fuels. As a matter of fact, the spontaneous ignition of directly-injected Diesel leads to a combustion process that is heterogeneous by nature, therefore characterized by the simultaneous production of particulate matter and NOx. In this scenario, several innovative combustion techniques have been investigated over the past years, the goal being to benefit from the high thermal efficiency of compression-ignited engines, which results primarily from high Compression Ratio and lean and unthrottled operation, while simultaneously mitigating the amount of pollutant emissions. To achieve these goals, gasoline Partially Premixed Combustion, an innovative combustion methodology mainly characterized by the high-pressure direct injection of gasoline in a CI engine, proved to be very promising. This work analyzes the combustion process produced by a multi-jet pattern which introduces gasoline in a light-duty compression-ignited engine installed in a test cell. The engine has been modified to operate in stable operating conditions over its whole operating range. Since this combustion methodology is very sensitive to cylinder thermal conditions, the stability of the optimized multi-jet pattern has been guaranteed directly by controlling the intake conditions, i.e. intake temperature and pressure. Experimental tests have been carried out at very different loads to highlight how the control parameters of interest affect the combustion process. Several tests, run in stable conditions (optimized injection pattern), have been compared to quantify the impact of injection pressure variations on combustion efficiency and emissions. The obtained results demonstrate that the optimal management of the injection pressure is a key parameter for combustion optimization and for the limitation of combustion impulsiveness, necessary to comply with the reliability limitations over the whole engine operating range.

This work focuses on the development and validation of a data-driven model capable of predicting the maximum in-cylinder pressure during the operation of an internal combustion engine, with the least possible computational effort. The model is based on two parameters, one that represents engine load and another one the combustion phase. Experimental data from four different gasoline engines, two turbocharged Gasoline Direct Injection Spark Ignition, a Naturally Aspirated SI and a Gasoline Compression Ignition engine, was used to calibrate and validate the model. Some of these engines were equipped with technologies such as Low-Pressure Exhaust Gas Recirculation and Water Injection or a compression ignition type of combustion in the case of the GCI engine. A vast amount of engine points were explored in order to cover as much as possible of the operating range when considering automotive applications and thus confirming the broad validity of the model. The validation process was carried out using bothf mean data from each explored engine point as well as cycle-by-cycle data, focusing on onboard application and the model implementation in a combustion control strategy. The validation also includes lean operating conditions for one of the SI engines, case in which lambda had to be added as a third input variable. The main scope of this work is to analyze the robustness of the model when being applied on these particular engine operating technologies and conditions (EGR, WI, lean and GCI combustion). In all cases, the model demonstrated to be accurate within 5% when considering both mean values and cycle-by-cycle data, while retaining its simplicity and low computational weight. Additionally, a study on the minimum amount of engine points necessary for the model calibration has been conducted and it was concluded that only about 20 engine points are needed, if chosen strategically as regards engine load and combustion phase.

The stringent emission regulations for Internal Combustion Engines (ICEs) spawned a great amount of research in the field of innovative combustion approaches characterized by high efficiency and low emissions. Previous research demonstrate that such promising techniques, named Low-Temperature Combustion (LTC), combine the benefits of Compression Ignition (CI) engines, such as high compression ratio and unthrottled lean mixture, with low engine-out emissions using a properly premixed air-fuel mixture. Due to longer ignition delay and high volatility compared to diesel, gasoline-like fuels show good potential for the generation of a highly premixed charge, which is needed to reach LTC characteristics. In this scenario, gasoline Partially Premixed Combustion (PPC), characterized by the high-pressure direct injection of gasoline, showed good potential for the simultaneous reduction of pollutants and emissions in CI engines. However, previous research on gasoline CI highlight that a key factor for the optimization of both efficiency and pollutants is the proper management of Exhaust Gas Recirculation (EGR). This work presents the experimental investigation performed running a light-duty CI engine, operated with gasoline PPC, and varying the mass of recirculated gases trapped in the combustion chamber. To guarantee the stability of gasoline autoignition in all the tested conditions, a specific experimental layout has been developed to accurately quantify the amount of trapped residual gases due to the internal and external EGR. The obtained results clearly highlight the impact of EGR on the combustion process and emissions, demonstrating that optimization of charge dilution with EGR is fundamental to guarantee the optimal compromise between efficiency and emissions over the whole operating range.

Nowadays, compression-ignited engines are considered the most efficient and reliable technology for automotive applications. However, mainly due to the current emission regulations, that require increasingly stringent reductions of NOx and particulate matter, the use of diesel-like fuels is becoming a critical issue. For this reason, a large amount of research and experimentation is being carried out to investigate innovative combustion techniques suitable to simultaneously mitigate the production of NOx and soot, while improving engine efficiency. In this scenario, the combined use of compression-ignited engines and gasoline-like fuels proved to be very promising, especially in case the fuel is directly-injected in the combustion chamber at high pressure. The presented study analyzes the combustion process produced by the direct injection of small amounts of gasoline in a compression-ignited light-duty engine. The engine under investigation has been modified to guarantee a stable engine operation over its whole operating range, that is achieved controlling boost pressure and temperature, together with the design of the injection pattern. Experimental tests have been performed to highlight the impact of several control variables on the combustion effectiveness, i.e. on combustion efficiency and ignition delay. To identify the main mechanisms which impact the start of the combustion process and the sensitivity to the variation of the main control parameters, several tests have been run, directly-injecting constant amounts of gasoline in a compression ignited engine. These tests have been performed changing intake pressure and temperature (when suitable to maintain combustion stability), fuel pressure and injection timing within the cycle.

Over the past years, the increasingly stringent emission regulations for Internal Combustion Engines (ICE) have led to the development of non-conventional combustion strategies like Low Temperature Combustions (LTC) characterized by high efficiency and low pollutant emissions. One of the most relevant LTC strategies is the Reactivity Controlled Compression Ignition (RCCI), characterized by the combustion of a lean mixture composed by air and a low reactivity fuel (LRF, gasoline in the case under study) ignited by a high reactivity fuel (HRF, Diesel in this study), directly injected in the combustion chamber, due to the high pressure and temperature in the cylinder. The proper management of this combustion strategy results in high efficiency and low engine-out emissions, with the simultaneous mitigation of both nitrogen oxides (NOx) and particulate matter (Soot). On the other hand, this combustion methodology is affected by high instability and high sensitivity to slight variations of the in-cylinder thermal conditions. Previous works demonstrate that combustion stability can be guaranteed through closed-loop control strategies that vary the injection parameters to keep the center of combustion (CA50, i.e. the angular position when the 50% of fuel burned within the engine cycle) at a proper target value. Although the center of combustion can be directly evaluated from in-cylinder pressure measurement, the on-board installation of in-cylinder sensors is still uncommon, mainly because they would increase the cost of the whole engine management system. Due to the above considerations, two different closed-loop control strategies have been developed by the authors of this paper to evaluate combustion characteristics using low-cost sensor, that are already present on-board for other management purposes. The current work summarizes these different strategies and demonstrate how a feed-forward estimation of the ignition delay, based on the estimation of the in-cylinder temperature, can improve the transient behavior of the control and how it is possible to replace all the information from in-cylinder pressure signal.