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.

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.

In the past years, stringent emission regulations for Internal Combustion (IC) engines produced a large amount of research aimed at the development of innovative combustion methodologies suitable to simultaneously reduce fuel consumption and engine-out emissions. Previous research demonstrates that the goal can be obtained through the so-called Low Temperature Combustions (LTC), which combine the benefits of compression-ignited engines, such as high compression ratio and unthrottled lean operation, with a properly premixed air-fuel mixture, usually obtained injecting gasoline-like fuels with high volatility and longer ignition delay.Gasoline Partially Premixed Combustion (PPC) is a promising LTC technique, mainly characterized by the high-pressure direct-injection of gasoline and the spontaneous ignition of the premixed air-fuel mixture through compression, which showed a good potential for the simultaneous reduction of fuel consumption and emissions in CI engines. Despite its potential, gasoline PPC might suffer from low combustion controllability and stability, because gasoline spontaneous ignition is significantly affected by slight variation of the local in-cylinder thermal conditions.This paper summarizes the work carried out to optimize gasoline PPC in a light-duty CI engine, operated in a test cell. The investigated system has been slightly modified to guarantee a stable operation, using gasoline instead of diesel, over a wide load range. The first part of the analysis has been focused on the study of gasoline auto-ignition, the goal being to define an injection strategy suitable to guarantee combustion stability. Then, further activity has been focused on performance investigation through a properly defined span of the main control parameters of interest, such as injection pressure and exhaust gas recirculation.

Reactivity-Controlled Compression Ignition (RCCI) combustion is considered one of the most promising Low-Temperature Combustion (LTC) concepts aimed at reducing greenhouse gases for the transportation and power generation sectors. Due to the spontaneous combustion of a lean, nearly homogeneous mixture of air and low-reactivity fuel (LRF), ignited through the direct injection of a small quantity of high-reactivity fuel (HRF), RCCI (dual-fuel) shows higher efficiency and lower pollutants compared to conventional diesel combustion (CDC) if run at very advanced injection timing. Even though a HRF is used, the use of advanced injection timing leads to high ignition delays, compared to CDC, and generates high cycle-to-cycle variability, limited operating range, and high pressure rise rates at high loads. This work presents an experimental analysis performed on a heavy-duty single-cylinder compression ignited engine in dual-fuel diesel–natural gas mode. The objective of the present work is to investigate and highlight the correlations between combustion behavior and pollutant emissions, especially unburned hydrocarbons (HC) and oxides of nitrogen (NOx). Based on the analysis of crank-resolved pollutants measurements performed through fast FID and fast NOx systems under different engine operating conditions, two correlations were found demonstrating a good accordance between pollutant production and combustion behavior: Net Cyclic Hydrocarbon emission—cyclic IMEP variations (R² = 0.86), and Cyclic NOx—maximum value of the Rate of Heat Released (R² = 0.82).