Cold start performance refers to a fuel’s ability to initiate and maintain combustion after a period of engine in-activity. In these instances, the engine chamber walls and fuel injection equipment are colder than their designed operating temperatures. Engines operating with poor cold performance fuels may be difficult to start and produce significant amounts of unwanted emissions including unburned hydrocarbons, carbon monoxide and partial combustion products such as aldehydes.
Glycerol, a major component of EHF technology, has poor combustibility (flash point >160°C) and benefits from a “pilot” or co-fuel to sustain combustion under normal engine operation. In EH technology, diesel fuel serves as the pilot to maintain efficient glycerol combustion. It is known, however, that if glycerol is not properly combusted, it may thermally decompose to form acrolein, a toxic aldehyde emission. Cold start performance has been a critical research area for EH technology, as this condition has the potential to produce acrolein emissions.
Cold Start Emission Tests on EHF Fuels
To address these concerns, SCG conducted a series of cold start emission tests using a Hatz 1B30z single-cylinder diesel engine and a heated exhaust dilution/sampling tunnel as shown in Figure 1. The dilution tunnel is heated to 90°C and dilutes the engine exhaust 25:1 with ultra-zero air to preserve exhaust chemistry to sampling. Toxic engine emissions such as acrolein and other aldehydes are captured using DNPH filters.
Figure 1. Cold start performance engine testing apparatus with heated engine exhaust dilution/sampling tunnel. The apparatus is used to compare amounts of various exhaust constituents, such as acrolein, from EH fuel and ultra-low sulfur diesel combustion
Cold start emission tests were completed in quadruplicate for both an EH20 fuel (20% volume glycerol) and ultra-low sulfur diesel. A modified EPA TO-11a test method was followed for the sampling of engine exhaust done at SCG’s research facility and for cartridge extraction and quantification conducted by Test America at their Phoenix, AZ laboratory. None of the samples detected the presence of acrolein indicating that EH technology maintained sufficient combustion temperatures, even under the most severe conditions. Figure 2 shows the average of each exhaust component identified resulting from the quadruplicate cold start tests for each fuel.
The major exhaust constituents were formaldehyde and acetaldehyde, with minor amounts of propionaldehyde detected. EHF fuels produced less toxic emissions than the base fuel ultra-low sulfur diesel (ULSD).