EU-PEMS PM Evaluation Program - First Report

The European legislation has adopted the Portable Emissions Measurement Systems (PEMS) as a tool to check the conformity of heavy-duty engines during their real operation. The current developments foresee the verification of gaseous emissions. The measurement and the control of in-service Particulate Mass (PM) emissions using on-board equipment has been delayed, as the technological status of the portable PM instrumentation had been judged insufficient. The European PEMS PM project was launched in 2007. Its main objective was to assess the technological status of the PEMS PM equipment. Initially, the main requirements set for the candidate instruments were: - to measure the PM mass, possibly according to existing standards; - to be designed for on-board testing regarding handling, test durations and power consumption; - to be advanced prototypes or commercially available equipment. An additional but important requirement was introduced: to be able to evaluate the in-service emissions (which is done in the United States through the Not To Exceed (NTE) approach), the European legislation has adopted a moving averaging window method. For such calculations, the accumulated PM mass had to be measured or estimated at any time during a test. The strategy used to evaluate the candidate instruments was simple and empirical. Using different engines, test cycles and fuels, the candidates were required to provide the best possible correlation with the reference laboratory systems. This ¿laboratory to portable¿ comparison was carried out for to the total PM mass measurements. The real-time PM results have been cross-correlated. In parallel to the program, some Particle Number (PN) measurements have been performed using equipment and test procedures in line with the European standards developed to test light-duty vehicles. This abstract provides the main findings of this project regarding PM, as presented and discussed in the final report of the European PEMS PM program. Furthermore, it gives the engine PN emissions and provides a first clue regarding the feasibility of PN for in-service testing. Different PM PEMS were evaluated in the lab with 3 heavy-duty engines which cover a wide range of emissions. The PM differences were in general 15% lower (SPC, OBS, micro-PSS) than the PM measured with a full dilution tunnel. Higher differences (35%) were found for MSS which measures soot. For the DPF engine the differences were >50% due to the volatile artifact on the filter. The PN differences between CVS and SPC were for all engines (and emission levels) within 15%. In addition to the PN method (non-volatiles measured with a CPC), MSS and DC were found to be sensitive enough at the low emission levels (post DPF). ETaPS and DMM (with dilution) were not sensitive enough for DPF engine. The conclusion of this work is that mass (on a filter) is not sensitive enough for low emission engines and the number method should be preferred. If PEMSs continue to use the filter method, then the real time instrument they use can affect the calculation factor as each instrument measures different particle property (number, surface, mass). Nevertheless, all these parameters do not affect the result enough to exceed the 10 mg/kWh limit of the future European HD regulation. They should be however seriously taken into account for lower emission levels.JRC.DDG.H.4-Transport and air qualit

Particle Matter Measurements for Inspection/Maintenance Programs

Particle emissions from Heavy Duty Diesel Vehicles (HDDVs) are currently measured by opacity or dynamometer gravimetric analysis. The Electronic Tailpipe Particle Sensor (ETaPS) is an inexpensive measurement device purported to give real time response to particle mass and was proposed as a possible addition to Inspection/Maintenance (I/M) programs. There were three goals to this study. The first was to verify ETaPS response to particle mass of HDDV exhaust. Integrated ETaPS signal was plotted against filter weight from dynamometer gravimetric analysis and a correlation was found. The second goal was to find a correlation between ETaPS readings and the Remote Sensing Detector (RSD). These tests were invalidated due to interference from power lines greatly affecting the ETaPS signal. The final goal was to find a relationship between the RSD and the dynamometer gravimetric analysis. Comparisons were made from averaged RSD smoke data, and averaged gravimetric data for each HDDV undergoing both tests. A measurable difference was found for RSD smoke readings between Diesel Particle Filter (DPF) equipped vs. non-DPF and DPF bypassed HDDVs

Two Decades of Maude

This paper is a tribute to José Meseguer, from the rest of us in the Maude team, reviewing the past, the present, and the future of the language and system with which we have been working for around two decades under his leadership. After reviewing the origins and the language's main features, we present the latest additions to the language and some features currently under development. This paper is not an introduction to Maude, and some familiarity with it and with rewriting logic are indeed assumed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Overfitting in Synthesis: Theory and Practice (Extended Version)

In syntax-guided synthesis (SyGuS), a synthesizer's goal is to automatically generate a program belonging to a grammar of possible implementations that meets a logical specification. We investigate a common limitation across state-of-the-art SyGuS tools that perform counterexample-guided inductive synthesis (CEGIS). We empirically observe that as the expressiveness of the provided grammar increases, the performance of these tools degrades significantly. We claim that this degradation is not only due to a larger search space, but also due to overfitting. We formally define this phenomenon and prove no-free-lunch theorems for SyGuS, which reveal a fundamental tradeoff between synthesizer performance and grammar expressiveness. A standard approach to mitigate overfitting in machine learning is to run multiple learners with varying expressiveness in parallel. We demonstrate that this insight can immediately benefit existing SyGuS tools. We also propose a novel single-threaded technique called hybrid enumeration that interleaves different grammars and outperforms the winner of the 2018 SyGuS competition (Inv track), solving more problems and achieving a $5\times$ mean speedup.Comment: 24 pages (5 pages of appendices), 7 figures, includes proofs of theorem

Parallel bug-finding in concurrent programs via reduced interleaving instances

Concurrency poses a major challenge for program verification, but it can also offer an opportunity to scale when subproblems can be analysed in parallel. We exploit this opportunity here and use a parametrizable code-to-code translation to generate a set of simpler program instances, each capturing a reduced set of the original program’s interleavings. These instances can then be checked independently in parallel. Our approach does not depend on the tool that is chosen for the final analysis, is compatible with weak memory models, and amplifies the effectiveness of existing tools, making them find bugs faster and with fewer resources. We use Lazy-CSeq as an off-the-shelf final verifier to demonstrate that our approach is able, already with a small number of cores, to find bugs in the hardest known concurrency benchmarks in a matter of minutes, whereas other dynamic and static tools fail to do so in hours

Improved Methodologies in Modeling and Predicting Failure in AASHTO M-180 Guardrail Steel Using Finite Element Analysis - Phase I

Steel guardrail systems have historic and widespread applications throughout the nation’s highways and roadways. However, catastrophic system failure can occur if the guardrail element ruptures, thus allowing an errant vehicle to pass uncontrolled through the system and potentially allow fractured ends to pierce the occupant compartment. To aid in the analysis and design of guardrail systems, further efforts are needed to develop and implement more reliable material failure criteria to predict and model guardrail steel rupture under all vehicle impact loading scenarios within impact simulation finite element method (FEM) software, such as LS-DYNA. This Phase I study accomplished a number of tasks to aid in this objective. First, historical and state-of-the-art failure criteria with emphasis on stress state dependent failure criteria were reviewed. Next, various failure surface methods that provide estimations on the triaxiality and Lode parameter vs. effective plastic strain at failure were review and analyzed. It was determined that more flexible failure surface fitting methods may provide better estimations, and larger more diverse testing programs are required to estimate the failure surface through all stress states. A failure surface method using a Smoothed, Thin-Plate Spline was also proposed to overcome short comings in existing failure surface estimation methods. Based on the review of the existing failure surfaces’ performance, a steel material testing program was developed, and testing was performed on 21 different specimen configurations that represent a range of stress states. The specimens were prepared using ASTM A572 Grade 50 steel with similar material properties as AASHTO M-180 guardrail steel. Test results and calculated material properties were presented herein. Lastly, a preliminary FEM modeling effort was conducted. Various modeling parameters were examined, including the effects from hourglass controls, mesh-size effects, inertial effects from load rate, and solid vs. shell behavior. Based on this analysis, preliminary models of the testing specimen were developed. Also, a preliminary material model was calibrated and presented herein. Conclusions were made, and recommendations were provided for continuing a Phase II effort. Advisor: Ronald K. Falle