Mercedes Mullins
Pilot fuel quantity is an important parameter for controlling the combustion process in a dual fuel engine. Pilot diesel injection timing (PDIT) plays a crucial role in the subsequent development of natural gas flame combustion. PDIT determines the premixing time and ignition moment of the combustible mixture in the cylinder. The quantity of pilot fuel can impact thermal efficiency and exhaust emissions. For example, in a dual producer gas-diesel engine, increasing the amount of pilot fuel improves thermal efficiency and reduces CO emissions at low engine load conditions. In another example, a diesel-ignited natural gas marine dual-fuel engine showed that advancements in PDIT increased the engine's power, thermal efficiency, and natural gas flame spread velocity, but also increased NO and CH4 emissions.
| Characteristics | Values |
|---|---|
| Engine speed | 1000 rpm |
| Pilot fuel quantity settings | 0.15, 0.19, 0.23 kg/h |
| Pilot fuel quantity settings | 0.125, 0.252, 0.312 MPa BMEP |
| Engine load | 0.503 MPa brake mean effective pressure (BMEP) |
| Engine type | Gardner 1L2 CI four-stroke, single-cylinder DI diesel engine |
| Engine performance | Higher brake thermal efficiency (35%) |
| Emissions | Lower NOx (60 ppm) and THC (0.4%) emissions |
| Higher exhaust emissions in dual-fuel mode |
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What You'll Learn
Pilot fuel quantity and its impact on combustion
The quantity of pilot fuel is an important parameter for controlling the combustion process in a dual-fuel engine. Pilot fuel quantity has a significant impact on the combustion process, engine performance, and emissions characteristics.
Imran et al. studied the effects of pilot fuel quantity on combustion and exhaust emissions in a dual-fuelled DI diesel engine. They found that increasing the pilot fuel quantity reduced ignition delay due to the creation of more ignition centres, which shortened the time between fuel injection and ignition. Additionally, they observed that increasing pilot fuel quantity reduced CO and HC emissions at low engine load conditions. This reduction in emissions is attributed to the larger volume of the charge affected by the combustion of the pilot fuel envelope, resulting in a higher burned fraction of the gaseous fuel.
In another study, Abd-Allah et al. examined the impact of pilot fuel quantity on a dual-fuel engine using methane or propane as the main fuel and diesel as the pilot fuel. They found that at very light loads with small pilot fuel quantities, CO and HC emissions were relatively high due to an excessively lean mixture. As the pilot fuel quantity increased, the combustion of the pilot fuel envelope affected a larger volume, improving the burned fraction of the gaseous fuel and reducing CO and HC emissions.
The size of the pilot fuel also plays a crucial role in the performance and exhaust emissions of dual-fuel engines, especially at light loads. It is desirable to replace liquid diesel fuel with clean and economical gaseous fuel. However, the quantity of pilot fuel must be maintained above a certain value to ensure continuous combustion of the gaseous fuel. Diesel fuel injection systems often experience poor atomization and deteriorated combustion when the amount of fuel injected per cycle falls below 5-10% of the ultimate design level.
Furthermore, the effect of pilot fuel quantity on ignition timing and combustion stability cannot be overlooked. The plume-blocking approach, a methodology used to investigate spray morphology, demonstrated greater penetration than the thimble-equipped nozzle method. This highlights the significance of optimizing pilot fuel injection methods to enhance combustion stability and overall engine performance.
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Pilot diesel injection timing
The quantity of pilot fuel is an important parameter for controlling the combustion process in a dual-fuel engine. Pilot diesel injection timing is one of the fundamental means of achieving reductions in NOx emissions. Adjustments in injection timing can also be used in conjunction with other control measures to ensure regulatory NOx limits are met.
In a dual-fuel engine, ignition of the main fuel is typically controlled by directly injected liquid pilot fuel. The liquid pilot fuel's initial penetration and total mass considerably impact exhaust emissions and combustion stability. The quantity of pilot fuel also has an impact on the engine's performance, combustion, and emissions characteristics. For example, in a dual producer gas-diesel engine, increasing the amount of pilot fuel improves thermal efficiency and reduces CO emissions at low engine load conditions.
However, the diesel saving is always decreased when the pilot fuel quantity exceeds its optimum condition. Additionally, too early an injection will lead to diesel spray impingement and poor atomization quality due to lower in-cylinder temperature and pressure. In a biodiesel-CNG dual fuel engine, the injection timing affects the combustion and emissions characteristics, with reduced nitrogen oxides, particulate matter, and smoke influenced by engine load, blend ratio, and injection timing.
Overall, the use of pilot fuel in a dual-fuel engine can have both positive and negative impacts on engine performance, combustion, and emissions. The specific effects depend on various factors such as engine load, blend ratio, injection timing, and the quantity of pilot fuel used.
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Pilot fuel and its effect on engine performance
Pilot fuel is an important parameter for controlling the combustion process in a dual-fuel engine. The quantity of pilot fuel can impact the performance and emissions of a dual-fuel engine.
In a dual-fuel engine, two different types of fuel are used simultaneously to power the engine. One fuel acts as the main fuel, while the other is used as the pilot fuel. The main fuel is typically a gaseous fuel, such as natural gas or methane, while the pilot fuel is usually a liquid fuel, such as diesel. The pilot fuel is injected into the combustion chamber, where it auto-ignites and creates ignition sources for the main fuel to burn.
The quantity of pilot fuel can affect the combustion stability and exhaust emissions of a dual-fuel engine. If the quantity of pilot fuel is too low, it can result in an excessively lean mixture, leading to incomplete combustion and higher carbon monoxide (CO) and hydrocarbon (HC) emissions. On the other hand, if the quantity of pilot fuel is too high, it can decrease diesel savings and negatively impact engine efficiency. Therefore, finding the optimal quantity of pilot fuel is crucial for achieving the best engine performance and emissions.
Several studies have been conducted to investigate the effect of pilot fuel quantity on engine performance. One study used a single-cylinder, direct injection, diesel engine coupled with a dynamometer to test the engine performance at different pilot fuel quantities. The results showed that increasing the amount of pilot fuel improved thermal efficiency and reduced CO emissions at low engine load conditions. Another study examined the effects of pilot fuel quantity on a dual-fuel engine using natural gas as the main fuel and diesel as the pilot fuel. They found that increasing the quantity of pilot fuel reduced the ignition delay and improved combustion stability.
In addition to the quantity of pilot fuel, the injection timing of the pilot fuel can also impact engine performance. For example, in a two-stage auto-ignition mode, optimizing the injection timing of the pilot fuel can lead to higher brake thermal efficiency and lower emissions.
Overall, the pilot fuel quantity and injection timing are important factors that can significantly affect the performance and emissions of a dual-fuel engine. Further research is needed to fully understand the complex interactions between these parameters and their impact on engine performance.
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Pilot fuel's role in dual-fuel engines
Pilot fuel is an important parameter for controlling the combustion process in a dual-fuel engine. The quantity of pilot fuel is significant, as it must be kept above a certain value to maintain continuous combustion of the gaseous fuel. The size of the pilot fuel also impacts the performance and exhaust emissions of dual-fuel engines.
In a dual-fuel combustion process, the ignition of the main fuel is typically controlled by directly injected liquid pilot fuel. The liquid pilot fuel's initial penetration and total mass impact exhaust emissions and combustion stability. The ignition of the main fuel plays a crucial role in engine performance and emissions.
The pilot diesel injection timing (PDIT) is significant in a dual-fuel engine. PDIT determines the premixing time and ignition moment of the combustible mixture in the cylinder. Advancing the PDIT increases the engine's power, thermal efficiency, and natural gas flame spread velocity, but it also increases NO and CH4 emissions. PDIT also affects the ignition delay period and the rapid combustion period.
Research has shown that engine performance, combustion, and emissions characteristics in two-stage auto-ignition mode are better than those in conventional diesel ignition mode. Pilot diesel injection timing can be optimized to yield higher brake thermal efficiency and lower NOx and THC emissions.
Dual-fuel engines can be designed with two injectors or a single injector. With two injectors, the pilot injector is separate from the gas injector, while with a single injector, the pilot injector is part of a combined unit with the gas injector. Dual-fuel engines using diesel as the pilot fuel can match the brake power and fuel economy of engines operating on pure diesel fuel.
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Pilot fuel's influence on exhaust emissions
Pilot fuel data for diesel refers to the use of diesel as a pilot fuel in dual-fuel engines. Pilot injection is a technique used in diesel engines to inject a small amount of fuel before the main injection to improve combustion and reduce emissions. The quantity and timing of pilot injection can significantly impact the performance, combustion, and emissions of an engine.
The influence of pilot fuels on exhaust emissions has been the subject of several studies. One study found that increasing the pilot injection quantity led to an increase in the size and number of soot agglomerates, resulting in higher soot mass. This increase in soot was attributed to the higher number of particles in the agglomerate and their larger average radius of gyration.
The dwell time between pilot injection and main injection also plays a crucial role in emissions. One study investigated the effects of different dwell times on a single-cylinder DI diesel engine fuelled with diesel or dimethyl ether (DME). They found that pilot injection effectively lowered heat-release rates, regardless of the fuel type. Additionally, DME showed lower NOx emissions with combustion retardation, while diesel had higher smoke emissions in pilot-main injection conditions compared to single-injection conditions.
The type of pilot fuel used in dual-fuel engines can also impact exhaust emissions. For example, when using methane or propane as the main fuel and diesel as the pilot fuel, it was observed that at very light loads and low pilot fuel quantities, CO and HC emissions were relatively high due to partial oxidation. However, as the pilot fuel quantity was increased, the combustion improved, resulting in reduced CO and HC emissions.
Furthermore, the use of dual-fuel engines with NG (natural gas) or hydrogen as the main fuel and diesel as the pilot fuel has been studied. It was found that increasing the quantity of pilot fuel reduced the ignition delay, potentially due to the creation of more ignition centres. Additionally, at high speeds and loads, the effect of pilot fuel quantity on emissions becomes less significant as the NG quantity is sufficient to produce a stable flame.
Overall, the quantity and timing of pilot injection, as well as the type of pilot fuel used, can significantly influence exhaust emissions. Pilot injection has the potential to reduce heat-release rates, lower NOx and THC emissions, and improve thermal efficiency, especially in two-stage auto-ignition modes. However, it can also lead to increased smoke and soot emissions, depending on the fuel type and operating conditions.
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Frequently asked questions
Pilot fuel is the initial fuel that is injected to ignite the main fuel in a dual-fuel engine.
Pilot fuel data for diesel involves studying the effects of varying pilot fuel quantities on the performance and emissions of diesel engines.
Pilot fuel data for diesel is important because it helps optimize engine performance, improve thermal efficiency, and reduce harmful exhaust emissions.
Key findings suggest that increasing the quantity of pilot fuel can improve thermal efficiency and reduce CO emissions at low engine load conditions. However, excessive pilot fuel quantities can lead to decreased diesel savings. Additionally, dual-fuel mode operation with oil-coir-pith had higher specific energy consumption and exhaust emissions compared to neat diesel/oil operation.
One challenge is that there is limited research on the detailed effects of pilot fuel quantity, especially in dual producer gas-diesel engines. Additionally, for large-scale low-speed dual-fuel marine engines, the traditional research method of data collection through numerous tests has space and equipment limitations.
