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Diesel fuel injection system is the most important part of the direct-injection diesel engine and, in recent years, it has become one of the critical technologies for emission control with the help of electronically controlled fuel injection. Common rail injection system has great flexibility in injection timing, pressure and multi-injections. Many studies and applications have reported the advantages of using common rail system to meet the strict emission regulation and to improve engine performance for diesel engines. The main objective of this study is to investigate the effect of pilot-, post- and multiple-fuel injection strategies on engine performance and emissions. The study was carried out on a single cylinder optical direct injection diesel engine equipped with a high pressure common rail fuel injection system. Spray and combustion evolutions were visualized through a high speed charge-coupled device (CCD) camera.

Efforts have been made to apply biogas to an IC engine for power generation as a way to cope with the energy crisis as well as to reduce greenhouse gas. However, due to its gas component variations by origin and low energy density, using biogas in the engine applications and achieving a steady power generation is not an easy task. One way to overcome these deficiencies is to add hydrogen in biogas. Because of the excellent combustion characteristics of hydrogen, use of hydrogen-biogas blend fuel can allow not only accomplishing stable in-cylinder combustion, but also reducing the harmful emissions such as THC and CO. Despite several advantages of this approach, there exists a major drawback~a significant increase in NOx emission caused by high adiabatic combustion temperature of hydrogen.

Because of the concerns regarding global warming caused by greenhouse gases and the high cost of fossil fuels, research on improving the fuel economy and emissions in internal combustion engines has become important. Specifically for spark ignition engines, lean-burning direct injection is the most promising technology because the fuel economy and emissions can be improved using a stable combustion of a stratified mixture. This study aimed to develop a spray-guided, lean-burning liquefied petroleum gas (LPG) direct injection engine through optimizing the combustion parameter controls. In previous research, the brake thermal efficiency in an LPG direct injection engine was significantly increased and stable combustion was secured with an interinjection spark ignition (ISI) strategy under low-load operating conditions.

Nowadays, automobile manufacturers are focusing on reducing exhaust-gas emissions because of their harmful effects on humans and the environment, such as global warming due to greenhouse gases. Direct injection combustion is a promising technology that can significantly improve fuel economy compared to conventional port fuel injection spark ignition engines. However, previous studies indicate that relatively high levels of nitrogen oxide (NOx) emission were produced with gasoline fuel in a spray-guided-type combustion system as a result of the stratified combustion characteristics. Because a lean-burn engine cannot employ a three-way catalyst, NOx emissions can be an obstacle to commercializing a lean-burn direct injection engine. Liquefied petroleum gas (LPG) fuel was proposed as an alternative for reducing NOx emission because it has a higher vapor pressure than gasoline and decreases the local rich mixture region as a result of an improved mixing process.

Natural gas produced from coal or biomass is known as synthetic natural gas (SNG), which is expected to replace compressed natural gas (CNG). In this study, we used an 11-l heavy-duty CNG engine in a feasibility study of SNG. SNG, which is composed of 90.95% methane, 6.05% propane, and 3% hydrogen, was produced for the experiment and used as fuel to estimate its effects on combustion and emission characteristics. The torque, fuel flow rate, efficiency, fuel consumption, combustion stability, combustion phase, and emissions characteristics obtained using SNG were compared to those obtained using CNG in an engine speed range of 1,000-2,100 rpm under full load conditions. In addition, an engine fueled with SNG was given an overall evaluation using the World Harmonized Stationary Cycle (WHSC) emission test. The engine's knock characteristic was analyzed at 1,260 rpm under a full load condition. The results showed that there was no difference in power output.

To counteract the harmful effects of vehicle emissions on humans and the environment, such as global warming due to greenhouse gases, there is a focus on gaseous fuels as an alternative energy source of transportation. Heavy-duty natural gas vehicles are widely used to improve the air quality of urban areas in Korea because natural gas has the advantage of low greenhouse gas emission levels. However, more in-depth study is required in order for clean fuel vehicles to hold a dominant position over well-developed diesel vehicles. It is difficult to meet reinforced emission standards with only a lean combustion strategy without an aftertreatment system in a lean-burn natural gas engine. Hydrogen-natural gas (HCNG) blends have been proposed as an alternative to improve fuel economy and emissions of lean-burn natural gas engines, since they have a wider flammability range and faster burning speed. HCNG blends could also play a role as a technical bridge for the hydrogen era.