Emissions

The emissions of nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbon (HC), and smoke were measured for the baseline Jet A, and the 25% and 50% Bio-SPK blends. The blends contained the same Jet A that was used as baseline fuel. The emissions test hardware (Figure 3-15), the data reduction and the test/analysis procedures closely approximated, and in most cases were identical with, the emissions certification testing hardware and procedures. The exhaust sampling system consisted of one stationary rake with three sampling orifices (probes) of equal size located at the core exit.

The portion of each sampling system outside the core exhaust stream was heated, as were the transfer lines, which led to the gas analysis equipment in the emissions trailer to avoid condensation.

(a)

(c) (b)

(a) Emissions Trailer, (b) Emissions Installation, (c) Emissions Probes

Figure 3-15. Emissions Set-up

The test point schedule for general thrust settings at which emissions test data was collected included the International Civil Aviation Organization (ICAO) take-off, climb, approach, and idle thrust settings (i.e., 100%, 85%, 30%, and 7%) that will be referred to as the landing and take-off (LTO) cycle herein after. The same point schedule was followed for the baseline fuel and the blends.

The gaseous emissions data was interpreted in terms of the Emissions Index (EI), which is calculated on the basis of grams of emission for a kilogram of burned fuel (g/kg). For each of the tests, the recorded EIs and the sampled FARs were obtained from the ganged-element gas samples gathered from the gas sample rakes. The ratio between the measured exhaust sample FARs and the calculated FARs derived from the measured fuel flow and computed engine core airflow was less than 8%, well within the limits (+/- 10% at take-off, climb, and approach; +/- 15% at idle) specified by ICAO⁸⁴. The variation in ambient conditions such as the temperature and wind conditions were small enough that their potential impact on results can be considered within the overall

uncertainty of the test. The procedure to get from raw measured emissions to engine characteristic emissions is given below in simplified form:

1) Correct EI values for variation in operating conditions for pressure and humidity in the case of NOx, and for variation in operating conditions for pressure in the cases of CO and HC.

2) Multiply emissions index (EI) by time in each flight mode (0.7 minutes for take-off, 2.2 minutes for climb, 4.0 minutes for approach, and 26.0 minutes for idle) and cycle fuel flow (kg fuel/hour) to obtain grams of pollutant.

3) Add grams of pollutant for 100%, 85%, 30%, and 7% for total mission pollutants.

4) Divide total grams of pollutant by thrust (kN) to obtain characteristic emissions (g/kN).

The smoke emissions were characterized by means of SAE Smoke Number (SN).

The highest SN from the four LTO ICAO points, typically the take-off value, is taken to be the characteristic SN for a particular engine rating. The results depicted in Figure 3-17 for 18K and 27K engine ratings reveal a reduction in NOx and smoke emissions with Bio-SPK addition to the conventional jet fuel, although the impact on NOx emissions (~1-5%) can be considered quite small, especially considering the level of uncertainty associated with the test. This impact on NOx and smoke is consistent with expectations as NOx generation in the gas turbine combustor is known to be thermal in nature (i.e., thermal-NOx is dominant over prompt-NOx and no fuel-bound NOx is present as fuels in consideration are Nitrogen-free), and the addition of Bio-SPK increases the Hydrogen/Carbon ratio (H/C) of the overall blend as is shown in Figure 3-16, decreasing the flame temperature and the thermal-NOx with it⁸⁵.

1.75 1.80 1.85 1.90 1.95 2.00 2.05 2.10 Continental Jet-A

25% Jatropha-Algae, 75% Continental Jet-A

50% Jatropha-Algae, 50% Continental Jet-A

100% Jatropha-Algae

H/C Molar Ratio

UOP GE AFRL

NB: collected by various Labs

Figure 3-16. H/C Molar Ratios for Baseline Jet A, Neat Bio-SPK, and Blends of the Two

This observation seems to be supported by the observed slight reductions in the EGT in the ground engine test during the emissions testing sequence. Similarly, smoke generation is inversely proportional with H/C, and directly proportional with the aromatic content, the former increased with the Bio-SPK addition, and the latter reduced with the addition as the Bio-SPK is aromatic-free. Thus the observed reduction in smoke is not unexpected either.

-40%

Figure 3-17. LTO Emissions and Maximum Smoke Number for Test Blends as % Difference from Jet A for Lowest (18K) and Highest (27K) CFM56-7B Engine Ratings

The impact on NOx is more pronounced with the 50% blend compared to the 25%

blend most likely due to the resulting lower flame temperatures with further Bio-SPK addition due to the H/C ratio differences between the baseline and the Bio-SPK. The smoke data however, indicates that the impact of blending 50% compared to 25% does not change the smoke reduction for higher thrust rating. The reason behind this is not easily anticipated and would require further investigation. CO and, to a greater extent, HC emissions are highly variable because the emissions levels are low (near the instrument calibration limit for HC), and these emissions can be influenced by small variations in engine state and ambient conditions. For example, considerable hysteresis has been noted as the engine “warms up”. Therefore, the large variation in HC levels cannot necessarily be attributed to fuel properties. However, in addition to the possible test variation the observed increase in CO and HC emissions might also be explained by the reduction in flame temperature, as the level of these emissions typically increase with decreasing flame temperature, stemming from the fact that colder temperatures will lead to more incomplete carbon oxidation. The impact of Bio-SPK addition appears to be more severe for the HC than the CO, but yet was still within regulatory requirements. A peculiar trend between CO and HC is also observed. While the CO emissions increase as more Bio-SPK is added (i.e., 50%/50% vs. 25%/75%) the opposite is true for the HC, as its emissions seem to get lower (Figure 3-17). This observation is not easy to understand, however, it should be remembered that the flame temperature is not the only mechanism that impacts the CO and HC emissions. The CO and HC emissions generation is very local in nature and known to be heavily impacted by the fuel spray (atomization) quality, which depends on surface tension, viscosity, and specific gravity of the fuel, all of which being different for each blend to a certain extent. In fact, changes in fuel surface tension and viscosity can be significant as the engine warms up, because there is a fuel-oil heat exchanger that heats the fuel as the oil heats up. Even in the case where the spray quality is the same, the flame location may differ due to flame speed differences possibly impacting emissions. Currently, the impact of the Bio-SPK addition on the atomization and the flame location, and respective effects of these modifications on the emissions of

CO vs. HC is not well known, but these tests indicate the impact could be significant, and is worthy of further study.

To summarize the emissions results, the addition of the Bio-SPK to the conventional jet fuel was found to have insignificant effects on emissions. The resulting emissions values for the test blends meet the current regulatory requirements. There was a slight reduction in NOx (~1-5%), and an increase in the CO (~5-9%) and HC emissions (~20-45%). While some parts of the observed changes to emissions are due to measurement variability, they are primarily explained by the anticipated reduction in the flame temperature. Additionally, the impact on spray quality and flame location is also expected to play a major role for emissions levels, especially for CO and HC. Lower smoke emissions (~13-30%) were also observed. Some part of this is understood as a result of the reduction in the aromatic content of the blends compared to the conventional jet fuel. The emissions may vary among various Bio-SPKs and the current results should be taken to be specific to the Bio-SPK tested. However, the variation in emissions among various Bio-SPKs is not expected to be extensive based on the consistency of the compositions reported for currently available Bio-SPKs. Further studies on the impact of the modifications of physical and chemical properties of the jet fuel by Bio-SPK addition on emissions are encouraged.

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Figure 3-18. LBO Historical Data Comparison

The LBO margin of Jatropha fuels is comparable to typical production engines.

Corrected Core Speed

Fuel Flow Ratio -7B Production Engines

874-026/4A - Jet A

874-026/4A - 25%/75% Blend 874-026/4A - 50%/50% Blend Increasing

LBO Margin

Figure 3-19. Warm Start Comparison

The warm start characteristics are unchanged.

Figure 3-20. Cold Start Comparison

The cold start characteristics are slightly improved with Jatropha mixes.

Time Corrected Core Speed (N2) EGT Fuel Flow (Wf)

Jet A 25%/75% Blend 50%/50% Blend

N2

Wf EGT

Time Corrected Core Speed (N2) EGT Fuel Flow (Wf)

Jet A 25%/75% Blend 50%/50% Blend

N2

Wf EGT

Figure 3-21. Accel Time Comparison

The acceleration characteristics are unchanged.

3.4.2.3 Rolls-Royce RB211-524G2-T Engine Ground Run