Comparison of Neat Biodiesels and ULSD in an Optimized Single-Cylinder Diesel Engine with Electronically-Controlled Fuel Injection

Abstract

Biodiesel can be produced from a variety of feedstock oils and, as a result, may have a diverse set of properties based on the oil used to produce it. An understanding of the effects of these properties on engine usage and emissions is needed in order to improve biodiesel production and engine calibration. In this study, four biodiesels, produced from palm, jatropha, soybean, and beef tallow oil, are used to fuel a single-cylinder compression-ignition engine to investigate the effects of individual fuel properties on combustion phasing and behavior and exhaust emissions. This engine uses a common-rail fuel system with electronic control. Electronic control of injection is used to investigate the effects of biodiesel on combustion when combustion phasing is adjusted. Findings indicate that fuel viscosity, energy content, and molecular structure are all critical properties that alter engine combustion behavior. The combined effect of injection timing and biodiesel characteristics is found to produce lower NO x emissions compared to ultralow-sulfur diesel.

Influence of Fuel Injection System and Engine-Timing Adjustments on Regulated Emissions from Four Biodiesel Fuels

“…Palm biodiesel has a lower level of unsaturated (double-bond) carbons in its composition than either soybean or canola oil, which has been theorized to improve NO x emissions by reducing energy release, and thus thermal NO x production (23). In an earlier study with the EI setup, a beef tallow biodiesel with similar FAME composition as palm also had lower NO x emissions than the more unsaturated fuels (16). These results are also consistent with the differences in soy and animal-based biodiesel NO x emissions recorded in the most recent California Air Resources Board study (9).…”

“…More recently, the team conducted additional emissions studies with four identical fuels (palm, soybean, canola, and coconut oil biodiesel) in the same engine after installation of an electronic fuel injection system. [Results of the soybean and palm biodiesel tests with the electronic fuel injection system were published previously in Mangus et al (16)]. This study analyzed the new and existing data to provide a unique assessment of how changes in the fuel injection system and engine timing can affect emissions of NO x and partial combustion products from identical biodiesel fuels in a simple engine system where variables can be more easily isolated.…”

Investigating the compression ignition combustion of multiple biodiesel/ULSD (ultra-low sulfur diesel) blends via common-rail injection

“…Biodiesel carries inherent advantages over ULSD based on its production from renewable sources and specific fuel properties, like higher lubricity, which reduces engine wear [6]. While biodiesel may be used in CI engines in neat form [2,7], the more common usage is as blends since it is miscible with ULSD [3,8e11]. This is because the low volatility of neat biodiesel causes issues with the post-injection process required for diesel particulate filter regeneration.…”

“…Since biodiesel is produced from a variety of feedstock oils, the effects of both neat and blended biodiesel fuels must be better understood to improve both fuel performance and engine operation [2,16]. In particular, differences in fuel viscosity, molecular structure, and energy content can alter the combustion process in multiple, often interacting, ways [2,3,7,18]. For example, viscosity increases with molecular carbon chain length.…”

“…This behavior, combined with biodiesel's typically higher cetane number rating, can advance combustion timing resulting in greater cylinder temperatures, and thus higher potential for in-cylinder NO x formation [27]. However, recent research performed by the authors with a single-cylinder Yanmar engine upgraded to a high-pressure rail fuel injection system found a decrease in NO x emissions when using neat biodiesel after normalizing combustion by maintaining consistent peak pressure timing between ULSD and biodiesel [7]. These results suggest that increased NO x emissions are not an inevitable feature of biodiesel use, but can be mitigated by adjusting engines to compensate for fuel-induced changes in combustion timing [7,25,27].…”