SeaChange Group LLC, in collaboration with the Maine Maritime Academy’s Marine Engine Testing and Emissions Laboratory (METEL), has demonstrated EHF combustion and emissions performance on a “tier 3” compliant Caterpillar marine engine. The goal of the project was to quantify combustion performance and emission reduction benefits of EHF fuel blends compared to ultra-low sulfur diesel fuel. Results demonstrate that EHF fuels are well suited for modern marine engines. Engine brake efficiency was increased by about 5% while reducing NOx and PM emissions. It is expected that EHF fuels can be used by any marine diesel engine to offset fossil fuel consumption and reduce unwanted air emissions.
Tests were performed at METEL facilities using a CAT 2.2L “tier 3” emissions compliant engine. The engine is a 4-cylinder direct injection engine with water cooling and turbocharging in genset configuration. The engine is mounted on a floating engine platform operating in hybrid-electric mode. For this test, the vessel was stationary mounted in the METEL facility and instrumented. The engine operates at a constant speed of 1,800 RPM and fueling rate was varied from idle to full load (27 kW). Power output from the genset was absorbed using an Avtron Freedom model 100 resistive element load bank with step sizes resolution of 3.75 kW. A photograph of the engine setup at METEL’s facility can be found in Figure 1. Engine specifications can be found in Table 1. The engine was equipped with gravimetric smoke monitoring and with a Bacharach PCA3 combustion analyzer for CO, NO, and NO2 emissions monitoring.
Figure 1. CAT 2.2 engine and hybrid-electric vessel located at METEL facilities in Bucksport, Maine.
The engine utilized a custom fuel switching scheme to allow the engine to operate on either ultra-low sulfur diesel (ULSD) or EHF fuels as shown in Figure 2. Fuel rate was monitored volumetrically. EH30 fuel (30% glycerol by mass) was prepared using an Emulsiflex C-50 high pressure homogenizer capable of processing pressures up to 30,000 psi and a peak processing rate of 12 gallons per hour of EHF fuel. A photograph of the Emulsiflex fuel processing system is shown in Figure 3 and Table 2 provides a comparison of the relevant EHF fuel properties compared to ultra-low sulfur diesel. EHF fuels are shown to have a lower energy density than traditional petroleum fuels. This is because glycerol’s heating value is approximately 40% that of diesel fuel. However, glycerol is 55% by mass oxygen, which lowers the stoichiometric air-to-fuel ratio improving combustion efficiency and fuel economy when emulsified in diesel fuel.
Smoke emissions were sampled gravimetrically using Millipore fiberglass filters. Particulates were sampled from the engine exhaust at a flow rate of 4 L/min for a total of 30 seconds. Soot present in the sample was collected on the 0.7 micron fiberglass filters and weighed. As seen in Figure 4, filters collected for ULSD and EH30 over the power settings from idle to full load provide visual evidence for the PM reduction behavior of EH fuels. This is attributed to excess oxygen in the fuel which limits the formation of soot precursors.
EHF fuels incorporate glycerol into diesel fuel in lower the stoichiometric air-fuel ratio and reduce adiabatic flame temperature. As such, NOx emissions are reduced by 12% during idle conditions and approximately 20% at full load as shown in Figure 5.
Glycerol has a lower energy density than ULSD, the overall energy density of the EH30 fuel blend is about 20% less on a MJ/kg basis resulting in higher fuel consumption as shown in Figure 6(A). Thermal efficiency benefits of EH30 fuel however, offsets much of the fuel consumption as shown in Figure 6(B). Therefore, fuel consumption at idle conditions is equivalent, while fuel consumption at full engine load in only increased by 9%. Glycerol is a low-value co-product of biodiesel manufacturing. It is expected that EHF fuels will be a cost effective alternative to fossil fuels with the additional benefit of lower NOx and PM emissions.