Quantification of Imaging Measurement Uncertainty for Gasoline Direct Injection Sprays

Transcription

1 ILASS Americas, 2 rd Annual Conference on Liquid Atomization and Spray Systems, Ventura, CA, May 20 Quantification of Imaging Measurement Uncertainty for Gasoline Direct Injection Sprays Lee E. Markle*, Ashley L. Lanos, Carlos A. Ospina, and Francis E. Brado Technical Center Rochester Powertrain Systems Division, Delphi Automotive Systems, LLC West Henrietta, NY USA Abstract Digital spray imaging is a measurement technique used to characterize the geometries of sprays including those from gasoline direct injection (G-DI) fuel injectors. While SAE J2 provides a procedure for standardized testing, currently there is no generally accepted standard protocol for defining the measurement uncertainty of the fuel injector spray parameters of spray angle and penetration. This work describes the development of a method to define and document the error present in the measurement of these key parameters of fuel spray characterization. A Six Sigma problem solving methodology provided the framework for investigating the uncertainty and ultimately for refining the testing procedure. With the increasingly stringent fuel economy and emissions requirements for automobiles, spray characteristic tolerances and limits are appearing on fuel injector specification documents. There is a need to more rigorously define the measurement error of the spray testing results, including spray geometry. Digital spray imaging is a technique frequently used in the automotive industry because of its ability to quickly generate global spray geometry characteristics. While digital spray imaging techniques can be used to generate data cost-effectively, the repeatability of data is rarely reported and a protocol for determining uncertainty in spray image measurements has not been previously detailed. Determining the measurement uncertainty can aid business decisions and avoid costly retesting. In this work, the sprays from representative test injectors were imaged many times consecutively on the Generation G-DI imaging system under evaluation. The resultant geometric data was used to document a statement of measurement error with a confidence level of %. This data also allowed for identification of common cause variation, special cause variation and validated the measurement and analysis process. Additionally, a measurement system analysis (MSA) was performed on the Generation G-DI imaging system to separate measurement system error from test injector variability. The MSA was accomplished by analyzing images from sprays and of a set of reference solid cones. These cones were created to represent a range of geometries similarly found in G-DI sprays. The resultant spray and cone image data sets were used to determine the G-DI imaging measurement system repeatability, equipment resolution, measurement linearity and measurement bias. Lastly, to monitor the G-DI imaging measurement system stability and consistency, representative reference injectors were identified and their sprays were imaged regularly over several months to determine the long-term measurement variation in the fuel injector spray parameters of spray angle and penetration. The lessons learned are being implemented for an improved-capability, Generation 2 G-DI imaging system. * Corresponding author: lee.e.markle@delphi.com

2 Definition of the Problem Introduction Today s gasoline direct injection (G-DI) fuel injectors are typically electromagnetic solenoid valves fitted with a multi-hole director plate for metering the fuel and atomizing and guiding the spray. The number and geometry of the holes is unique for the specific engine application of the fuel injector. As the fuel is delivered directly into the combustion chamber of the engine, the spray geometry is critical to avoid impingement on surfaces and to achieve the appropriate air /fuel ratio distribution before ignition. Engine developers typically specify the flow characteristics required of a fuel injector, as well as some basic spray geometry parameters, including spray angle and spray penetration []. The spray angle is a measure of the angular extent of a G-DI fuel spray, and is typically determined by shadowgraphy imaging. It is defined as the angle between the spray edges at the pre-determined locations near the injector tip at a specified time after the beginning of the visible presence of fuel; also know as start of fuel (SOF). See Figures and 2. The spray penetration is defined as the maximum distance along the injector axis between the leading edge of the spray and the tip of the injector, at a specified time after SOF. See Figure. Figure. Determination of SAE J2 Spray Angle and Penetration from Imaging Figure 2. Typical Shadowgraph Image and Analysis of a G-DI spray Digital spray imaging is a measurement technique used to characterize the geometries of sprays including those from G-DI fuel injectors. This technique is frequently used in the automotive industry because of its ability to quickly generate global spray geometry characteristics. The SAE Gasoline Fuel Injection Standards Committee has decided on the use of shadowgraphy in the recommended practice, SAE J2 for obtaining numerical characterization of fuel sprays. Shadowgraphy was chosen because Mie-scatter techniques cause small drops to be disproportionately over-represented in the image, confounding analysis [2]. SAE J2 further defines that the entire spray be imaged using a camera with a minimum pixel resolution of 000 X 000 pixels with a dynamic range of at least 26 levels of gray. A pulsed light source must have a duration of under µs. Furthermore, the image of the pulsed fuel spray is to be captured at. ms after SOF and the size of the image is to be such that the axial distance from the injector tip is 00 mm. While digital spray imaging techniques can be used to generate data quickly and cost-effectively, particularly when the same images are used to determine both the spray angle and penetration, the repeatability of data is rarely reported and a protocol for determining uncertainty in spray image measurements has not been previously detailed. SAE J2 provides a procedure for standardized testing, and makes a statement that all spray measurement tools should undergo repeatability and reproducibility testing. However, currently there is no generally accepted standard protocol for defining the measurement uncertainty of the fuel injector spray parameters of spray angle and penetration.

3 Methodology and Scope This work describes the development of a method to define and document the error present in measurement of spray angle and penetration. A Six Sigma problem solving methodology provided the framework for this measurement system analysis (MSA). Six Sigma is a set of practices originally developed by Motorola Incorporated to systematically improve processes and eliminate defects. It provides a structured, detailed and controlled framework for identifying problems and generating solutions and improvements. The DMAIC (Define the problem, Measure the process, Analyze the process, Improve the process, and Control the process) methodology is a continuous improvement roadmap which can be followed when an existing process with substandard performance is being improved upon. Define: As stated in the introduction, the problem is defined as the lack of quantification of the variation in the Generation G-DI digital spray imaging system. Measure: The baseline performance of the equipment is documented. In order to keep the testing of the fuel injectors repeatable, a detailed digital spray imaging process guaranteed that each test was performed in the same manner and permits further investigation of variation. Analyze: G-DI spray geometric imaging data was used to document a statement of measurement error with a confidence level of %. An MSA was also performed to quantify the measurement system error from the variability associated with the tested hardware. Also, the short-term and long-term measurement variation in spray angle and penetration were calculated. Improve: Opportunities for mitigating uncertainty were identified and addressed. Control: To monitor the G-DI imaging system measurement stability and consistency, representative reference injectors were identified and their sprays were imaged regularly over several months. The stability evaluation effort is still ongoing. This work describes the process used for determining the measurement uncertainty of a specific G-DI digital spray imaging system. However, the DMAIC process and analysis techniques described here can be extended to all digital spray imaging measurements and other spray measurement techniques as was previously demonstrated in the ILASS-Americas 2008 work, Quantification of Variation in Laser Diffraction Gasoline Fuel Injector Droplet Sizing []. Measure the Process Testing Protocol and Set-up The SAE J2 recommended practice dictates the imaging testing techniques and protocol, and the basic specifications for the imaging system components to be used for G-DI spray imaging. Per this recommendation, the Generation imaging system in this work uses the shadowgraphy technique. See Figure. To backlight the spray using visible light, an Nd:YAG laser operating at 2 nm, with a 0 mj, 0 ns pulse provided illumination to a diffuser system comprised of lenses and a translucent screen. The camera was an 8-bit MegaPlus.4i, with a resolution of 2 X 04 pixels. An inhouse-developed, National Instruments LabVIEW software with the IMAQ software kit was used to create the signal controls for the camera, laser and fuel injector, and for the collection and analysis of the images. The images captured were calculated to be 62.0mm (width) X 2.mm (height) in size. Therefore, the pixel resolution of the Generation imaging system is 0.2 mm / pixel. Figure. Basic Schematic of G-DI Shadowgraphy from SAE J2 The injectors were tested per an established inhouse measurement protocol derived from SAE J2. See Table and Figure 4. Fuel Type: n-heptane Injection Pulse Width:.ms Period (Injection Pulse and Camera Trigger): 00ms Image Delay:.ms after SOF Camera Exposure: 00ms Lens: 60mm F-stop: f4 Gain: 6 db Number of Pixels: 2 x 04 Image Size: 62.0 mm x 2. mm Pixel Resolution 0.2 mm / pixel Table. Generation Imaging System Parameters

4 Figure 4. Generation Imaging System G-DI Reference Fuel Injector The G-DI reference fuel injector used to evaluate the Generation imaging system was an inwardlyopening multi-hole fuel injector of a custom-design. The injector delivers 22 mg of n-heptane during a. ms pulse. A high resolution patternator was used to determine the footprint of the injector s 6 spray plumes and their orientation. This pattern was used to position the injector with respect to the camera of the imaging system. See Figure. Camera Figure. Spray Footprint of the G-DI Reference Injector Analyze the Process Diffuser Initial Estimation of Measurement Uncertainty After a thorough definition of the problem, per DMAIC methodology, the baseline performance of the Generation imaging system was determined. This was accomplished by capturing 0 images of the spray from the G-DI reference fuel injector at the same time after the SOF for each image. The number 0 was chosen to allow the data to approach a normal distribution per the Central Limit Theorem. By having a normal distribution of data, a wider range of statistical tools are applicable, allowing for the determination of the measurement s % confidence interval. Minitab statistical analysis software was used extensively for the analysis and the results described in this work [4]. The plots in Figure 6 and Figure display a sequence of spray angle and penetration Individual measurements and their corresponding Moving Ranges. These I-MR charts can illustrate the presence of issues with a measurement process. Using the standard deviation of the entire measurement data set (from 0 images), upper and lower control limits are calculated by adding to and subtracting from the average, three times the standard deviation. If individual measurements fall outside of the control limits, a special cause, or an unusual or unpredictable event, may be influencing the measurements. If the individual measurements fall within the control limits, the process is called statistically stable as only common cause variation from random, uniform fluctuations are influencing the measurements. The creation of these initial I-MR charts allowed for the following discoveries about the Generation imaging system / G-DI reference injector testing:. The difference between the upper and lower control limits of the I-MR plots illustrate the magnitude of measurement variability present between the individual images of the G-DI reference injector pulses. 2. Since the moving range plot contained several points with a zero value (two or more subsequent measurements resulted in the same value), the measurement system s resolution may need improvement.. The Generation imaging system with the G-DI reference injector testing is statistically stable, allowing further analysis to determine an estimate of uncertainty. To evaluate the capability of the measurement process a Type Gage Study was performed on the same initial measurements used for the I-MR plots. Among other statistical parameters, the Type Gage Study yields the measurement standard deviation; also known as the estimated total measurement error, S m. Using Minitab, this type of study was performed on both the spray angle and penetration measurements from Generation imaging system with the reference injector. The standard deviations were then doubled to estimate each geometric characteristic s % confidence interval, a statement of measurement uncertainty. The results are shown in Table 2. G-DI Reference Injector Geometric Parameter S m Type Gage Results % Confidence Interval Spray Angle ( ) 2.2 ±.84 Penetration (mm).60 ±.20 Table 2. Initial Estimation of Measurement Uncertainty for the Generation Imaging System / G-DI Reference Injector

5 Individual Value of Spray A ngle ( ) G-DI Reference Injector Spray Angle I-MR Chart Observation 28 UC L=8.42 X=4. LC L=4. Moving Range, Spray A ngle ( ) Observation UC L=0. MR=.8 LC L=0 Figure 6. Spray Angle Variation from the Generation Imaging System with G-DI Reference Injector Individual Value of Penetration (mm) G-DI Reference Injector Penetration I-MR Chart Observation 28 UC L=2.40 X=6. LC L=6.4 Moving Range, Penetration (mm) Observation UC L=.484 MR=.6 LC L=0 Figure. Penetration Variation from the Generation Imaging System with G-DI Reference Injector

6 These results combine the measurement system error and the G-DI reference injector variability. Also, it is important to note that these estimates of uncertainty contain limited sources contributing to variation: only one test set-up was used, only one operator performed the testing, the testing was performed on one day only, etc. As a result, it must be noted that these estimates of uncertainty reflect a best case. As the sources of variation are increased the estimate of uncertainty has the potential to also increase. Knowing that the estimated measurement error has both the Generation imaging system measurement uncertainty combined with the G-DI reference injector variability, work had to be performed to discern the contribution of only the measurement system. Estimation of Measurement System Uncertainty using Reference Solid Cones Cone Description Because the G-DI reference injector exhibited visible injection-to-injection spray geometry differences typical of inwardly-opening multi-hole fuel injectors, a stable geometric shape that resembled a spray was necessary. A dummy injector with the same internal and external dimensions as the reference injector was fabricated. In addition, solid stainless steel cones with extensions were created with different angles and penetrations lengths. These were made to span the historically observed range of spray angles and penetrations measured by the research laboratory. These cones were measured by the fabricator to determine corresponding geometric reference values. The dummy injector and a sample solid cone are shown in Figure 8. Figure 8. Typical Reference Solid Cone with Dummy G-DI Injector Three cones of different angles and three extension pieces of different lengths were made to span nominal spray angle geometries of 0, 0 and 0 and penetrations of 0 mm, 0 mm and 0 mm. Each combination of angle and length were measured by the fabricator and the values are shown in Table. Combination Length (mm) Angle ( ) 0 Cone 0mm Pen Cone 0mm Pen Cone 0mm Pen Cone 0mm Pen Cone 0mm Pen Cone 0mm Pen Cone 0mm Pen Cone 0mm Pen Cone 0mm Pen Table. The Fabricator s Measured Values of the Reference Cones and Penetration Extensions Combinations Cone Testing and Analysis As was performed during the initial estimation of measurement error with the G-DI reference injector, 0 images of the solid cones were taken consecutively on the Generation imaging system for each of the nine combinations. All of the combinations were then evaluated using I-MR charts for angle (spray angle) and length (penetration). The findings from the angle analyses were similar to that from the initial estimate evaluation for the reference injector. Namely:. The difference between the upper and lower control limits of the I-MR plots illustrate the magnitude of measurement variability present between the individual images of the reference metal cones. This magnitude corresponds to a variation of one pixel. 2. Since the moving range plot contained many points with a zero value, the resolution of the Generation imaging system needs improvement. The measurements were found to toggle between two discrete pixel locations.. The results obtained from the reference solid cones testing are statistically stable, allowing further analysis using a Type Gage Study to determine an estimate of the Generation imaging system s uncertainty. The findings for the penetration extension analysis were unlike those of the angle findings in that no measurement variation was observed. Unlike the variable penetration measurements for the G-DI reference injector, all 0 images of each cone / penetration extension combination gave the same length value. While these results show a high degree of precision due to lack of variation, no statistical methods could be employed.

7 Using the findings from the angle I-MR charts, the combination with the most variation was selected for further analysis using a Type Gage Study. The resultant Minitab analysis is shown in Figure. Gage name:.0 Generation Imaging Stand Highest Variability Cone / Penetration Extension Combination Run Chart Angle (degrees) Ref Observation Basic Statistics Reference 2.4 Mean 2.42 StDev * StDev (SV ) 2.08 Figure. Type Gage Study Angle Variation Results for the Highest Variability Combination of the Reference Solid Cones Similar to the G-DI reference injector, the Type Gage Study yielded the measurement standard deviation, S m. The standard deviation was then doubled to estimate the angle measurement s % confidence interval. The result is shown in Table 4. Again, because of the high precision of the penetration extension length measurements, uncertainty estimates for length (penetration) cannot be calculated. Solid Cones Geometric Parameter S m Type Gage Results % Confidence Interval Angle ( ) 0.4 ± 0.6 Table 4. Estimation of Measurement Uncertainty for the Generation Imaging System using the Reference Solid Cones It can be concluded from the reference solid cone study that the contribution of the measurement uncertainty from the Generation imaging system is a fraction of the total observed angular uncertainty (measurement system error plus product variability): 0.4 versus 2.2. Evaluating the Total Measurement Uncertainty for the Generation Imaging System From the Type Gage Study of the solid cones, it can be concluded that the product measurement error component is the larger contributor to the measurement uncertainty. The relatively large contribution of product variation, in comparison to the contribution of measurement system error, requires a method to mitigate the effects of the product variation on the measured value. In SAE J2, a method for minimizing injector spray variation is prescribed. It calls for averaging the geometric values obtained from a minimum of individual images to obtain one conglomerate value. For the G-DI reference injector, this method was followed and then repeated. To set upper and lower control limits on the geometric results, a minimum of repetitions is needed. For this work, measurements of more than twenty repeated results over a four month time span were evaluated. These results were processed using Minitab yielding an I-MR S (Between / Within) chart, where the between compares the conglomerate averages and the within compares the results from the individual im-

8 ages of each set. The top section of the chart is a graph monitoring control (within upper and lower control limits), and the bottom two sections of the chart allow for a determination of uncertainty. See Figure 0. G-DI Reference Injector Spray Angle I-MR-R/S (Between/Within) Chart Each Subgroup is Derived from Image Values Mean Spray Angle ( ) UCL=2.82 X=4.482 LCL=46.8 MR of Subgroup Mean ( ) UCL=4.0 MR=.2 LCL=0 2 UCL=6.264 Sample StDev ( ) S=2.8 LCL=0 Sample 2 Figure 0. G-DI Reference Injector Spray Angle from Images I-MR-R/S (Between/Within) Chart With the data obtained from Figure 0 (and a corresponding chart for penetration that is not shown here), the total measurement uncertainty was determined using Donald Wheeler s equation of long and short-term measurement error () []. Where short-term measurement error, denoted as S w, only includes limited contributions to variation. Long-term measurement error, denoted S b, includes the many sources of variation influencing the data over the four-month time span. The total measurement error, denoted S m, was calculated as follows. MR s b = d 2 d 2 =.28 MR is the average moving range between the mean of each run divided by d 2, a bias correction factor, employed for a subgroup size of 2 (consecutive runs), and equal to.28 [6] s w = S n = number of runs 2 sw s m = + () The results yielded from equation are contained in Table below. Reference Injector Average of Images Geometric Parameter n Uncertainty Estimate Table. Total Measurement Uncertainty for the Generation Imaging System with G-DI Reference Injector Improve the Process Reducing the Total Measurement Uncertainty by Mitigating the Effect of Product Variability Although the measurement uncertainty results for the SAE J2 minimum recommended number of averaged images () were determined, the opportunity to S m ( s ) 2 % Confidence Interval Spray Angle ( ).4 ±.4 Penetration (mm).0 ±.40 b

9 decrease variability between repeat conglomerate values was present without jeopardizing test throughput. This was accomplished by increasing the number of individual images within the conglomerate value from to 0. In a similar fashion as was performed with the images and shown in Figure 0, I-MR-R/S (Between/Within) charts for spray angle and penetration were created using 0 individual images from the G-DI reference injector. See Figures and 2 below. G-DI Reference Injector Spray Angle I-MR-R/S (Between/Within) Chart Each Subgroup is Derived from 0 Image Values Mean Spray Angle ( ) UCL=. X=4.66 LCL=4. 2 MR of Subgroup Mean ( ) 2 0 UCL=2.6 MR=0.2 LCL=0 2 UCL=4.4 Sample StDev ( ) 4 2 S=.4 LCL=.0 Sample 2 Figure. G-DI Reference Injector Spray Angle from 0 Images I-MR-R/S (Between/Within) Chart G-DI Reference Injector Penetration I-MR-R/S (Between/Within) Chart Each Subgroup is Derived from 0 Image Values 2 UCL=.82 Subgroup Mean 0 68 X=6.48 LCL=6. 2 MR of Subgroup Mean UCL=2.80 MR=0.88 LCL=0 2 Sample StDev UCL=.46 S= LCL=.0 Sample 2 Figure 2. G-DI Reference Injector Penetration from 0 Images I-MR-R/S (Between/Within) Chart

10 The data obtained from the I-MR-R/S (Between/Within) charts using 0 images enabled the utilization of the Wheeler equation to yield our final S m calculations for the Generation imaging system. See Table 6 below. Reference Injector Average of 0 Images Geometric Parameter S m Uncertainty Estimate Table 6. Total Measurement Uncertainty for the Generation Imaging with the G-DI Reference Injector Mitigating Product Variability Effects Clearly, the effect of increasing the number of analyzed images in the conglomerate averaged value mitigates the product variability portion of the total estimated uncertainty. Next, the calculated S m values were used to determine the equipment resolution. Measurement Resolution The equipment resolution is defined as the smallest increment that can be measured by the system. Understanding the measurement resolution is crucial to reporting meaningful and useful results. Wheeler, [] developed criteria that evaluates the effective resolution of a system. See equation 2, below. Equipment resolution 0.< <.0 (2) s m % Confidence Interval Spray Angle ( ) 0.8 ±.4 Penetration (mm) 0.0 ±.80 The minimum resolution of the Generation imaging system was observed in the imaging of the reference solid cones where the geometric values obtained toggled between those corresponding to one pixel. Reference Injector Spray Angle The spray angle resolution of the G-DI reference injector was calculated by averaging the angular changes caused by adding and subtracting one-pixel from the average Spray Angle value: X, 4.6. See Figure. SAE J2 specifies that the spray angle is calculated from four points on the boundary of the spray at mm and mm downstream from the injector tip. See Figure. The resultant change of a single pixel (with a pixel resolution of 0.2 mm / pixel) on a point on the SAE spray boundary yields a Spray Angle resolution of 0.8. The S m for the spray Angle is 0.8 and using Equation 2 shows that the Wheeler equation is satisfied with a value of Therefore the resolution is acceptable. Reference Injector Penetration The penetration resolution of the G-DI reference injector is simply equal to the pixel resolution of 0.2 mm. The S m for the penetration is 0.0 mm. Equation 2 is satisfied with a value of 0.4. As with the spray angle resolution, the penetration resolution is also acceptable. The Generation G-DI imaging system has acceptable resolution for measuring sprays typified by those from the G-DI reference injector. If this system were to be used for testing sprays from G-DI injectors that demonstrated little to no variability (approaching the repeatability of the reference solid cones), then the Generation G-DI imaging system could be found to have insufficient resolution. Discussion of Measurement Linearity and Measurement Bias It is important to verify that the measurement system is suited for use over the expected range of G- DI spray geometries. A linearity and bias study determines the performance with respect to this range. For the reference injector, it is impossible to know the true-value of the spray angle and spray penetration. However, for the reference solid cones, the Generation imaging system measurements can be compared to values obtained by other geometric assessments of this hardware. If the angle and length values provided by the cone fabricator are accepted as true, the measurement linearity (gain) and measurement bias (offset) of the Generation imaging system can be determined. Using Minitab, the geometric values from Table are compared to their corresponding imaging results using a gage linearity and bias study. See Figures and 4 below.

11 Gage Linearity and Bias Study: Penetration Length Gage Linearity and Bias Study: Angle Gage name: Generation Imaging System Gage name: Generation Imaging System 0.20 Regression % CI Regression % CI Data Avg Bias Data Avg Bias Bias (mm) 0.0 Bias ( ) Penetration Length (mm) A ngle ( ) 60 0 Figure. Generation Imaging System Angle Linearity and Bias Evaluation As can be seen in Figures and 4, the Generation imaging system seems to exhibit both linearity and bias concerns. The system seems to underestimate the spray angle and overestimate the spray penetration. Additionally, in both cases the amount of error is not a constant offset. A possible factor in the error is that the number of pixels used in the image analysis is too low, as was discussed in the Cone Testing and Analysis section where toggling of values was observed. A measurement system without linearity and bias problems will have a horizontal line across the tested region with no offset from the true values. Such is not the case with the Generation imaging system, but these issues are being addressed in the ongoing creation of a future G-DI imaging system. Control the Process Next Steps There is a plan to continue testing the G-DI reference injectors in order to monitor the Generation imaging system stability and consistency in reporting spray angle and penetration. With a larger number of points for the average conglomerate data, the upper and lower control limits for the spray angle and penetration can be fixed allowing the use of standard statistical control charts. An assumption was made that the cone fabricator provided angle and length values for the reference solid cones that were accurate. Cone measurements traceable to the National Institute of Standards and Technology (NIST) are planned to better assess the findings that the Generation imaging system has statistically significant bias and linearity issues. Figure 4. Generation Imaging System Penetration Length Linearity and Bias Evaluation Recommendations This work will be presented to the SAE Gasoline Fuel Injection Standards Committee for their consideration in future revisions to the minimum testing and analysis criteria of SAE J2. Given the expectation that G-DI injector sprays will become increasingly less variable, the Generation G-DI imaging system will be increasingly less capable. Its uncertainty will consume an ever larger portion of the tightening spray specification tolerances. A next generation system ( Generation 2 ) is being created with increased pixel resolution. An MSA of this new Generation 2 system will be performed, with the expectation of markedly reduced measurement uncertainty. Conclusions The Generation G-DI imaging system is an appropriate tool for measuring injectors typified by the G-DI reference injectors. The % confidence interval for spray angle is ±.4 and the % confidence interval for spray penetration is ±.80 mm. The resolution of the Generation imaging system is acceptable, but only because of the product variability typified by all inwardly-opening multihole G-DI injectors. This MSA work provides a roadmap for those needing to undertake similar spray measurement uncertainty determination. The DMAIC methodology provides guidance, not only for evaluating measurement uncertainty, but for improving and controlling it as well.

12 Acknowledgements The authors would like to acknowledge the support of individuals that provided guidance for this eight-month project. This includes statistical experts, Craig Smith and Mark Wirth. We are also grateful to our management, especially Tess Wallace, for their support and encouragement. References. Zhao, F., Harrington, D.L., Lai, M-C., Automotive Gasoline Direct-Injection Engines, SAE International, 2002, pp SAE International Surface Vehicle Recommended Practice J2, Gasoline Fuel Injector Spray Measurements and Characterizations, (200), SAE International, Warrendale, Pennsylvania. Chmiel, D.M., Ospina, C.A., Humphrey, W., et al ILASS Americas, 2st Annual Conference on Liquid Atomization and Spray Systems, Orlando, Florida, May 8-2, 2008, Session T-B Minitab Software v...0, StatGuide, Minitab, Incorporated, 200. Wheeler, D., EMP (Evaluating the Measurement Process) III: Using Imperfect Data, SPC Press, Wheeler, D., Lyday, R., Evaluating the Measurement Process, Second Edition, SPC Press, 8, p.4