The report was submitted to the New York State Energy Research Development Authority , the National Biodiesel Board and the National Oilheat Research Alliance . Released at the end of 2018 , the document gathers in one place numerous research projects looking at how biodiesel ( ASTM 6751 ) performs , at various blend levels , when combined with petroleum heating oil for space heating applications .

The introduction from the report (“ B20 to B100 Blends as Heating Fuels ”) appeared in the February 2019 issue of Fuel Oil News , beginning on page 24 . A second excerpt ( Part 2 ) appeared on page 14 of the March 2019 issue .

COMBUSTION PERFORMANCE AND FLAME SENSOR RESPONSE

Successful use of a fuel in home heating applications requires demonstration of acceptable combustion performance and satisfactory operation of the other combustion related components contained in a home heating oil system , particularly the flame sensor . Combustion of No . 2 heating oil in a home heating oil system is very different than combustion of No . 2 diesel fuel in a high-pressure compression ignition diesel engine , although heating oil and diesel fuel have very similar properties and are in many cases interchangeable .

In today ’ s diesel engines , the fuel typically passes through an on-board fuel filter with nominal pore size between 2 and 30 microns into a high-pressure common rail pump and is atomized through a multi-hole injector into a closed cylinder . The tolerances of the high-pressure fuel pump and injectors are very tight , as fuel injection pressures commonly exceed 20,000 psi .

In a home heating oil system , fuel passes through a strainer and gear pump into a retention head style burner with a swirl pressure nozzle . The fuel filter , upstream of the pump and strainer is commonly rated for 10 microns . The burner atomizes fuel at 100-150 psi into an open chamber fire box . Fuel is lit by an igniter located close to the burner nozzle which provides a spark similar to that of a spark plug in an engine , which initiates open flame combustion of the fuel oil . The hot gases then flow through the convective section of the boiler or furnace , transferring heat to the boiler water or air , and then exit through the flue . Home heating oil systems are much less complicated and operate at higher tolerances and much lower pressures than today ’ s high-performance diesel engines .

In comparison to the closed cylinder system in a diesel engine , heating oil systems are open-flame systems and excess air ( or excess flue gas oxygen , O2 ) is always used to ensure essentially complete combustion . The amount of excess flue gas oxygen to insure good combustion , generally between 3 % and 6 % excess O2 or 15 % and 40 % excess air to minimize smoke and ensure very low levels of carbon monoxide , is generally set by the installation technician when the burner is installed versus being controlled by an electronic control module found on diesel engines . The combustion performance and excess O2 level is normally re-checked on service calls or when the nozzles are replaced , typically once every one or two years .

In a home heating oil system , the key aspects of acceptable combustion include providing reliable ignition under field conditions , a flame which is stable and does not pulse substantially , low potential for formation of carbon deposits on burner head and nozzle tip , and low levels of exhaust smoke and CO . Since properly operating home heating oil systems burn the fuel completely in excess air and emissions are low , emissions are not regulated like those of gasoline or diesel engines although sulfur dioxide emissions are indirectly regulated through the fuel sulfur level . Due to this clean combustion , heating oil emissions are typically not measured or monitored , with the exception of smoke and CO which are used in the field to ensure the heating oil system is properly tuned to avoid the practical issues of particulate buildup on boiler tubes and any appreciable amount of carbon monoxide in the home .

Each home heating system is also equipped with a sensor that detects if a viable flame has been established and is being maintained as fuel is being sprayed into the fire box . Most flame sensors in home heating systems are relatively low-cost cadmium sulfide photoconductors ( commonly called a ‘ cad cell ’) which respond largely to visible light from incandescence in the combustion flame zone . This visible light is translated by the cad cell into a resistance value that can be used to stop the fuel flow in the event a flame is not established during ignition or is suddenly extinguished during normal operation .

Another option for flame sensing is photodiode-based systems . These have faster time response and can be used with a matched circuit to respond to the alternating part of the flame brightness signal . This provides better discrimination between the flickering light of a flame and the steady light from combustion chamber refractory . These sensors are commonly used in residential oil burners in Europe with highly recirculating burners which have less visible light . These sensors are also used in larger ( commercial ) boilers .

The goal of the work done in this area was to evaluate the proper atomization and combustion performance of biodiesel blends in conventional home heating oil burner systems and to determine any impacts of the presence of biodiesel on flame sensor operation and effectiveness .

Prior studies have shown that biodiesel flames emit less light overall than petroleum-based flames and this is largely a function of particulate concentration in the flame zone . This impact was also studied during this project .

EXPERIMENTAL

As discussed in the introduction section , a general review of the combustion performance is included in Appendix I . Generally , biodiesel blends have combustion performance similar or better than that of petroleum-based No . 2 oil . Biodiesel

12 APRIL 2019 | FUEL OIL NEWS | www . fueloilnews . com