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Overcharging lithium-ion batteries is a failure mode that is observed if the battery management system (BMS) or battery charger fails to stop the charging process as intended. Overcharging can easily lead to thermal runaway in a battery. In this paper, nickel manganese cobalt (NMC) battery modules from the Chevrolet Bolt, lithium manganese oxide (LMO) battery modules from the Chevrolet Volt, and lithium iron phosphate (LFP) battery modules from a hybrid transit bus were overcharged. The battery abuse and emissions tests were designed to intentionally drive the three different battery chemistries into thermal runaway while measuring battery temperatures, battery voltages, gaseous emissions, and feedback from volatile organic compound (VOC) sensors. Overcharging a battery can cause lithium plating and other exothermic reactions that will lead to thermal runaway.

Internal short-circuit in cells/batteries is a phenomenon where there is direct electrical contact between the positive and negative electrodes leading to thermal runaway. The nail penetration tests were used to simulate an internal short circuit within the battery, where a conductive nail was used to pierce the battery cell separator membrane which provided direct electrical contact between the positive and negative electrodes. The batteries tested during this work were common batteries used in existing automotive applications, and they included a nickel manganese cobalt (NMC) battery from a Chevrolet Bolt, a lithium manganese oxide (LMO) battery from a Chevrolet Volt, and a lithium iron phosphate (LFP) battery in a hybrid transit bus. The battery abuse and emissions tests were designed to intentionally drive the three different battery chemistries into thermal runaway while measuring battery temperatures, battery voltages and gaseous emissions.

Internal short-circuit in cells/batteries is a phenomenon where there is direct electrical contact between the positive and negative electrodes leading to thermal runaway. The nail penetration tests were used to simulate an internal short circuit within the battery, where a conductive nail was used to pierce the battery cell separator membrane which provided direct electrical contact between the positive and negative electrodes. The batteries tested during this work were common batteries used in existing automotive applications, and they included a nickel manganese cobalt (NMC) battery from a Chevrolet Bolt, a lithium manganese oxide (LMO) battery from a Chevrolet Volt, and a lithium iron phosphate (LFP) battery in a hybrid transit bus. The battery abuse and emissions tests were designed to intentionally drive the three different battery chemistries into thermal runaway while measuring battery temperatures, battery voltages and gaseous emissions.

This paper is part of a larger body of experimental and computational work devoted to studying the role of close-coupled post injections on soot reduction in a heavy-duty optical engine. It is a continuation of an earlier computational paper. The goals of the current work are to develop new CFD analysis tools and methods and apply them to gain a more in depth understanding of the different in-cylinder environments into which fuel from main- and post-injections are injected and to study how the in-cylinder flow, thermal and chemical fields are transformed between start of injection timings. The engine represented in this computational study is a single-cylinder, direct-injection, heavy-duty, low-swirl engine with optical components. It is based on the Cummins N14, has a cylindrical shaped piston bowl and an eight-hole injector that are both centered on the cylinder axis. The fuel used was n-heptane and the engine operating condition was light load at 1200 RPM.

The effects of spray targeting on mixing, combustion, and pollutant formation under a low-load, late-injection, low-temperature combustion (LTC) diesel operating condition are investigated by optical engine measurements and multi-dimensional modeling. Three common spray-targeting strategies are examined: conventional piston-bowl-wall targeting (152° included angle); narrow-angle floor targeting (124° included angle); and wide-angle piston-bowl-lip targeting (160° included angle). Planar laser-induced fluorescence diagnostics in a heavy-duty direct-injection optical diesel engine provide two-dimensional images of fuel-vapor, low-temperature ignition (H2CO), high-temperature ignition (OH) and soot-formation species (PAH) to characterize the LTC combustion process.

Recent measurements in transient diesel jets have shown that fuel in the wake of the injection pulse mixes with ambient gases more rapidly than in a steady jet. This rapid mixing after the end of injection (EOI) can create fuel-lean regions near the fuel injector. These lean regions may not burn to completion for conditions where autoignition occurs after EOI, as is typical of low-temperature combustion (LTC) diesel engines. In this study, transient diesel jets are analyzed using a simple one-dimensional jet model. The model predicts that after EOI, a region of increased entrainment, termed the “entrainment wave,” travels downstream at twice the initial jet propagation rate. The entrainment wave increases mixing by up to a factor of three. This entrainment wave is not specific to LTC jets, but rather it is important for both conventional diesel combustion and LTC conditions.

Low temperature combustion (LTC) strategies, which can mitigate emissions of particulate matter (PM) and nitrogen oxides (NOx) from diesel engines, typically have longer ignition delays compared to conventional diesel operation. With extended ignition delays, more time is available for premixing, which reduces PM formation. The effect of varying ignition delay on the spatial and temporal evolution of soot in LTC diesel jets is studied by imaging the natural soot luminosity, while the in-cylinder soot mass and temperature are measured using two-color soot thermometry. Ignition delay in the engine is controlled by adjusting the intake air temperature while keeping the same charge density at TDC. This allowed us to study sooting characteristics at various ignition delays while keeping the same diesel jet penetration for all the cases.

Low-temperature combustion (LTC) strategies for diesel engines are of increasing interest because of their potential to significantly reduce particulate matter (PM) and nitrogen oxide (NOx) emissions. LTC with late fuel injection further offers the benefit of combustion phasing control because ignition is closely coupled to the fuel injection event. But with a short ignition-delay, fuel jet mixing processes must be rapid to achieve adequate premixing before ignition. In the current study, mixing and pollutant formation of late-injection LTC are studied in a single-cylinder, direct-injection, optically accessible heavy-duty diesel engine using three laser-based imaging diagnostics. Simultaneous planar laser-induced fluorescence of the hydroxyl radical (OH) and combined formaldehyde (H2CO) and polycyclic aromatic hydrocarbons (PAH) are compared with vapor-fuel concentration measurements from a non-combusting condition.

In-cylinder and exhaust soot mass were measured in an optically accessible heavy duty diesel engine under various intake oxygen concentrations from 8 vol% to 21 vol% to gain insight into soot formation and destruction processes. Exhaust-gas recirculation (EGR) in the optical engine was simulated by dilution of intake gases with nitrogen. In-cylinder soot, measured by 2-color optical pyrometry, was compared to engine-out soot, measured by a commercial optical smoke meter. Each EGR rate was studied under two separate fueling conditions: (i) constant injection duration, and (ii) constant global equivalence ratio. The in-cylinder and exhaust soot measurements of the current study agree well with findings of previous studies in the literature. Under both fueling conditions, in-cylinder soot temperatures decreased with the reduction of in-cylinder oxygen concentration.

Although low-temperature combustion (LTC) strategies for compression-ignition engines can achieve very low emissions of nitrogen oxides (NOx) and particulate matter (PM) at high efficiency, they typically have increased emissions of other pollutants, including unburned hydrocarbons (UHC). In the current study, the equivalence ratio of mixtures near the injector are quantified under non-combusting conditions by planar laser-Rayleigh scattering (PLRS) in a constant-volume combustion chamber and by planar laser-induced fluorescence (PLIF) of a fuel tracer (toluene) in a single-cylinder direct-injection heavy-duty diesel engine at typical LTC conditions. The optical diagnostic images show that the transient ramp-down at the end of fuel injection produces a low-momentum, fuel-lean mixture in the upstream region of the jet, which persists late in the cycle.

In-cylinder spray, mixing, combustion, and pollutant-formation processes for low-load (4 bar IMEP), low-temperature combustion conditions (12.7% charge oxygen, ∼2170 K stoichiometric adiabatic flame temperature) with early fuel injection (SOI=-22° ATDC) at two different charge densities (naturally aspirated, 1.34 bar abs. boost) were studied in an optical heavy-duty diesel engine using simultaneous pairings of multiple laser/imaging diagnostics. Laser-elastic/Mie scattering showed liquid-fuel penetration, fuel fluorescence indicated the leading edge of the vapor jet, chemiluminescence imaging showed the location of ignition, OH fluorescence probed the hot second-stage combustion, and soot luminosity and soot laser-induced incandescence measured development of in-cylinder soot.

Three different approaches for modeling diesel engine combustion are compared against cylinder pressure, NOx emissions, high-speed soot luminosity imaging, and 2-color thermometry data from a heavy-duty DI diesel engine. A characteristic time combustion (KIVA-CTC) model, a representative interactive flamelet (KIVA-RIF) model, and direct integration using detailed chemistry (KIVA-CHEMKIN) were integrated into the same version of the KIVA-3v computer code. In this way, the computer code provides a common platform for comparing various combustion models. Five different engine operating strategies that are representative of several different combustion regimes were explored in the experiments and model simulations. Two of the strategies produce high-temperature combustion with different ignition delays, while the other three use dilution to achieve low-temperature combustion (LTC), with early, late, or multiple injections.

A 2003 heavy-duty diesel engine (2002 emissions level) was used to test a representative biodiesel fuel as well as the methyl esters of several different fatty acids. The fuel variables included degree of saturation, the oxygen content, and carbon chain length. In addition, two pure normal paraffins with the corresponding chain lengths of two of the methyl esters were also tested to determine the impact of chain length. The dependent variables were the NOx and the particulate emissions (PM). The results indicated that the primary fuel variable affecting the emissions is the oxygen content. The emissions results showed that the highest oxygen content test fuel had the lowest emissions of both NOx and PM. As compared to the baseline diesel fuel the NOx emissions were reduced by 5 percent and the PM emissions were reduced by 83 percent.

Although in-cylinder optical diagnostics have provided significant understanding of conventional diesel combustion, most alternative combustion strategies have not yet been explored to the same extent. In an effort to build the knowledge base for alternative low-temperature combustion strategies, this paper presents a comparison of three alternative low-temperature combustion strategies to two high-temperature conventional diesel combustion conditions. The baseline conditions, representative of conventional high-temperature diesel combustion, have either a short or a long ignition delay. The other three conditions are representative of some alternative combustion strategies, employing significant charge-gas dilution along with either early or late fuel injection, or a combination of both (double-injection).

It is generally accepted that thermal (Zeldo'vich) chemical kinetics dominate NO formation in diesel engines, so control of temperature is critical for reducing exhaust NOx emissions. Recent optical engine data revealed that when the start of injection (SOI) was retarded to very late timings, combustion luminosity decreased while exhaust NOx emissions increased, causing a “NOx bump.” This data suggested that changes in radiative heat transfer from soot may affect in-cylinder temperatures and subsequent NOx formation. In this study, soot thermometry measurements of in-cylinder temperature and radiative heat transfer were correlated with exhaust NOx to quantify the role of radiative heat transfer on in-cylinder temperatures and NOx formation. The engine was operated at low-load conditions, for which the premixed burn was a significant fraction of the total heat release.

Southwest Research Institute (SwRI) is exploring the feasibility of extending the performance and fuel efficiency of the spark ignition (SI) engine to match that of the emission constrained compression (CI) engine, whilst retaining the cost effective 3-way stoichiometric aftertreatment systems associated with traditional SI light duty engines. The engine concept, which has a relatively high compression ratio and uses heavy EGR, is called “HEDGE”, i.e. High Efficiency Durable Gasoline Engine. Whereas previous SwRI papers have been medium and heavy duty development focused, this paper uses results from simulations, with some test bed correlations, to predict multicylinder torque curves, brake thermal efficiency and NOx emissions as well as knock limit for light and medium duty applications.

SwRI has developed a new technology concept involving the use of high EGR rates coupled with a high-energy ignition system in a gasoline engine to improve fuel economy and emissions. Based on a single-cylinder study [1], this study extends the concept of a high compression ratio gasoline engine with EGR rates > 30% and a high-energy ignition system to a multi-cylinder engine. A 2000 MY Isuzu Duramax 6.6 L 8-cylinder engine was converted to run on gasoline with a diesel pilot ignition system. The engine was run at two compression ratios, 17.5:1 and 12.5:1 and with two different EGR systems - a low-pressure loop and a high pressure loop. A high cetane number (CN) diesel fuel (CN=76) was used as the ignition source and two different octane number (ON) gasolines were investigated - a pump grade 91 ON ((R+M)/2) and a 103 ON ((R+M)/2) racing fuel.

Homogeneous Charge Compression Ignition (HCCI) experiments were performed in a variable compression ratio single cylinder engine. This is the fourth paper resulting from work performed at Southwest Research Institute in this HCCI engine. The experimental variables, in addition to speed and load, included compression ratio, EGR level, intake manifold pressure and temperature, fuel introduction location, and fuel composition. Mixture preparation and start of reaction control were identified as fundamental problems that required non-traditional mixture preparation and control strategies. The effects of the independent variable on the start of reaction have been documented. For fuels that display significant pre-flame reactions, the start of the pre-flame reactions is controlled primarily by the selection of the fuel and the temperature history of the fuel air mixture.

A technology path has been identified for development of a high efficiency, durable, gasoline engine, targeted at achieving performance and emissions levels necessary to meet heavy-duty, on-road standards of the foreseeable future. Initial experimental and numerical results for the proposed technology concept are presented. This work summarizes internal research efforts conducted at Southwest Research Institute. An alternative combustion system has been numerically and experimentally examined. The engine utilizes gasoline as the fuel, with a combination of enabling technologies to provide high efficiency operation at ultra-low emissions levels. The concept is based upon very highly-dilute combustion of gasoline at high compression ratio and boost levels. Results from the experimental program have demonstrated engine-out NOx emissions of 0.06 g/hp/hr, at single-cylinder brake thermal efficiencies (BTE) above thirty-four percent.

It is generally accepted that exhaust NOX emissions of diesel engines increase with the degree of premixed burning. Although several mechanisms proposed in the literature are likely responsible for some aspects of the correlation, taken together, they cannot explain all observations of this correlation. In this study, thermodynamic analyses and optical/imaging diagnostics were employed in an optically-accessible, heavy-duty DI diesel engine to examine the in-cylinder mechanisms by which fuel/air premixing affects engine-out NOX emissions. Exhaust NO and NOX emissions were measured and correlated with observations of soot luminosity and jet penetration as the intake-temperature and injection timing were varied. The engine was operated at low-load conditions, for which the premixed burn was a significant fraction of the total heat released.