Fuel Chemical Analysis and Properties Research

NREL strives to more deeply understand how fuel properties impact engine operation. We accomplish this by relating fuel properties to fuel chemistry and molecular structure.

We evaluate a broad range of renewable gasoline and diesel fuels ranging from currently available ethanol and biodiesel to future products such as dimethyl furan and hydrotreated biomass pyrolysis oils.

Detailed Hydrocarbon Analysis of Gasoline Properties

For gasoline boiling range hydrocarbons, NREL applies detailed hydrocarbon analysis (DHA), which is a high-resolution gas chromatography method for identifying and quantifying more than 98% of the components of a petroleum refinery gasoline. This rich data set of chemical information can then be used to calculate useful properties.

Fuel Chemical Properties Data and Analysis

Our analytical and data science prowess plays a vital role in accelerating the pace of fuels and combustion research advancements.

About the Metric

The DHA-derived parameter particulate matter index (PMI) is a widely used metric for ranking the particulate matter formation tendency of gasolines, including gasolines containing biofuels. Particulate matter consists of fine particles that have negative impacts on human health. Their emissions from cars and trucks are regulated by government agencies worldwide.

PMI is calculated from the DHA, considering the properties of each individual component. NREL’s fuel chemistry and engine combustion research has shown that particle formation from biomass-derived oxygenates is not accurately predicted by PMI because some oxygenates have low energy barrier reaction pathways to soot formation. For more information, see engine combustion research.

Additionally, alcohols such as ethanol have a much higher heat of vaporization (HOV) than gasoline, and when blended into gasoline the increased evaporative cooling can cause more particles to form from the aromatic compounds in gasoline under some conditions. The DHA can also be used to calculate the HOV of complex mixtures such as gasoline-ethanol blends. Current research is exploring how to predict the distillation curve of gasoline from the DHA, as well as other properties.

Related Publications

Heat of Vaporization Measurements for Ethanol Blends Up To 50 Volume Percent in Several Hydrocarbon Blendstocks and Implications for Knock in SI Engines

Knock Resistance and Fine Particle Emissions for Several Biomass-Derived Oxygenates in a Direct-Injection Spark-Ignition Engine

Impact of Ethanol Blending into Gasoline on Aromatic Compound Evaporation and Particle Emissions from a Gasoline Direct Injection Engine

Metal Contaminants Impact Analysis on Diesel Emission Control Systems

Microwave-Plasma Atomic Emission Spectroscopy Analysis

NREL has developed methods for analysis of sodium and other metals to well below 1 part per million (ppm) (sodium detection limit of 0.023 ppm) using microwave-plasma atomic emission spectroscopy and inductively coupled plasma atomic emission spectroscopy. This research has shown that sodium levels in biodiesel on the market are typically well below 0.5 ppm. However, a small percentage of samples were as high as 3 ppm.

To learn more, read Metals Analysis of Biodiesel Blends.

Durability Testing and Physico-Chemical Characterization

In collaboration with Cummins, Inc., and Oak Ridge National Laboratory, NREL examined the impact of sodium on diesel emission control systems in a 1,000-hour accelerated durability test followed by detailed physico-chemical characterization of the emission control system components. 

It showed that at the currently allowed level of 5 ppm in 100% biodiesel the sodium doubles the rate of ash accumulation in the DPF (the balance is ash from the engine lubricant), increasing engine back pressure and resulting in increased NOx emissions.

A typical biodiesel contains sodium at less than 1 ppm. Nevertheless, industry stakeholders are considering measures to significantly reduce the sodium content in biodiesel.

To learn more about the study, read Evaluation of Fuel-Borne Sodium Effects on DOC-DPF-SCR Heavy-Duty Engine Emission Control System: Simulation of Full-Useful Life.

Metal Impurities and Their Challenges

Fuels can contain metal impurities, such as sodium and calcium, that end up in the engine exhaust.  They can also deposit on emission control system components—such as diesel oxidation catalysts, diesel particle filters, and NOx reduction catalysts—resulting in catalyst deactivation and filter clogging.

Biodiesel—a biofuel produced from vegetable oils, animal fats, and waste cooking oil—can contain sodium as a residue from its manufacturing process. Sodium is potentially present at levels below 1 ppm, making accurate analysis of the sodium content of a fuel a significant challenge.

Innovative Gasoline Heat of Vaporization Measurement Method

NREL has developed a method for measuring heat of vaporization (HOV) as the fuel evaporates using a differential scanning calorimetry/thermogravimetric analysis (DSC/TGA) instrument. The method has been applied to ethanol blends into the Fuels for Advanced Combustion Engines (FACE) A research gasoline.

Results show that adding ethanol increased the heat flow until the ethanol has evaporated, so there is less cooling during the later phase of evaporation. Ongoing research is examining more complex gasolines and the impact of azeotropic interactions between ethanol and gasoline boiling range hydrocarbons.

Fuel Direct Injection and Heat of Vaporization

Gasoline engines that use direct injection (DI) of the fuel currently make up approximately half of new cars sales in the United States. One of the advantages of DI is that the fuel evaporates in the engine cylinder, which lowers the temperature of the fuel-air mixture because of the fuels HOV. This evaporative cooling has several beneficial effects, including reducing pumping loss for induction of air into the engine and increasing the fuel’s effective knock resistance allowing increased compression ratio—both effects significantly improve engine efficiency. Alcohols such as ethanol have a much higher HOV than gasoline hydrocarbons (923 kilojoules per kilogram [kJ/kg] for ethanol versus 350 to 400 kJ/kg for gasoline). Thus, blending of ethanol increases HOV and results in even lower fuel-air mixture temperature.

While the total HOV of a gasoline ethanol blend can be calculated from the DHA, engine developers and combustion researchers need to understand how the HOV evolves as the fuel evaporates.

Related Publications

Heat of Vaporization Measurements for Ethanol Blends Up To 50 Volume Percent in Several Hydrocarbon Blendstocks and Implications for Knock in SI Engines

Heat of Vaporization and Species Evolution During Gasoline Evaporation Measured by DSC/TGA/MS for Blends of C1 to C4 Alcohols in Commercial Gasoline Blendstocks

Contact

To learn more about our work or explore partnership opportunities, contact Teresa Alleman or Gina Fioroni.