Spark Assistance Research Articles

Numerical Optimization of Spray-Guided Spark Assistance for Cold Idle Operation in a Heavy-Duty Gasoline Compression Ignition Engine

This article describes the results of a response surface model (RSM)-based numerical optimization campaign for spray-guided spark assistance at cold operations in a heavy-duty gasoline compression ignition (GCI) engine. On the basis of an earlier work on spark-assisted GCI cold combustion, a space-filling design of experiments (DoE) method was first undertaken to investigate a multitude of hardware design variables and engine operating parameters. The main design variables included the number of injector nozzles, fuel split quantities and injection timings, and spark timing. The objective variables were engine combustion efficiency (ŋc), maximum pressure rise rate (MPRR), and engine-out nitrogen oxide (NOx) emissions. A total of 150 design candidates were automatically generated using the Sobol sequence method provided by the commercial software package, CAESES. Then, closed-cycle computational fluid dynamic (CFD) spark-assisted GCI simulations under cold idling operations were performed. The outcomes from the CFD-DoE design campaign were utilized to construct high-fidelity RSMs that allowed for further design optimization of the spark plug- and fuel injector-related design variables, along with fuel injection strategy parameters. A merit function with respect to objective variables was formulated with an appropriate weight assignment on each objective variable. Finally, the best design candidate was identified from the RSM-based optimization process and further validated in the CFD analysis. The best design candidate showed the potential to significantly improve combustion efficiency (ŋc > 90%) over the baseline at cold idle while satisfying MPRR and NOx emissions constraints (MPRR < 5 bar/CAD and NOx < 4.5 g/kWh).

Potential of ozone addition on dethrottling of a gasoline/ethanol blend-fueled direct injection spark ignition engine in part load

Several efforts are required to improve engine efficiency and decrease global carbon dioxide (CO2) emissions and local pollutant products. In countries like Brazil, with a four-decade long experience with ethanol, the use of fossil fuels, although widespread, is being put under intense scrutiny. Governmental programs like ROTA 2030 stimulate engine research and development focused on environment-friendly fuels such as bioethanol-gasoline blends. Brazilian gasoline has about a quarter of ethanol, reducing the carbon footprint while maintaining suitable energy density. Regardless of the fuel, the load control method in part load operation of spark ignition engine causes a considerable penalty in fuel conversion efficiency. For these reasons, ozone addition was tested as an ignition enhancer that would allow higher de-throttling to reduce part-load pumping losses. The residual gas was used to dilute the mixture due to the possibility of keeping the three-way catalyst working properly with the stoichiometric mixture. An experimental investigation on efficiency, emissions and combustion related parameters was carried out in a downsized 1.0 l turbocharged direct-injected engine. Experimental tests were performed at 3 bar of indicated mean effective pressure (IMEP), 1500 rpm and stoichiometric air-fuel ratio. Spark timing (ST) was adjusted to achieve maximum indicated efficiency and the fuel used was Brazilian gasoline. Different ozone concentrations were used as a mixture with the intake air to overcome unstable engine operation by enhancing ignition. The results showed that it is possible to increase the gas exchange efficiency with ozone addition by promoting de-throttling operation with residual gases. Furthermore, the ozone addition exhibits the potential to promote autoignition of the end gas with spark assistance, even with a low compression ratio and residual gas fraction higher than 30%. However, the combustion efficiency is impaired by the higher residual gas fraction in some operation points that leave room for improvements.

Combustion control of DME HCCI using charge dilution and spark assistance.

To realize the potential of DME for clean combustion, fueling control is essential. In this research, the challenges, advantages, and applicability of high-pressure direct injection and low-pressure port injection are reviewed and evaluated, especially in relevance to HCCI combustion. In this study, emphasis is given to the applicable ranges of low-pressure fuel delivery in relevance to load, air-fuel ratio, and inert gas dilution, for realizing HCCI combustion. The strategy of high-pressure direct injection is advantageous for combustion phasing control, but the fuel handling is challenging because of the high vapor pressure of DME fuel. The strategy of port fuel injection is prone to early combustion and, consequently, tends to produce excessive pressure rise rates in the combustion chamber. This challenge is escalated at higher engine loads, making homogenous charge compression ignition difficult to achieve. In this paper, the load extension of DME-fueled HCCI combustion was explored. First, the impact of dilution on the combustion characteristics of DME HCCI was studied under lean and CO2 diluted conditions. Under the present empirical setups, results show that the lean-burn strategy has limited capability of combustion phasing control, especially when the engine load is above 5 bar IMEP. The CO2 dilution strategy can significantly retard the combustion phasing until the fulfillment of combustion becomes unstable. It was found that spark assistance is advantageous for combustion control. With an effective application of excess air, intake CO2 dilution and spark assistance, an engine load of 8 bar IMEP was reached with appropriate combustion phasing, with ultra-low NOx emissions.

CFD-Guided Evaluation of Spark-Assisted Gasoline Compression Ignition for Cold Idle Operation

A closed-cycle, three-dimensional (3D) computational fluid dynamics (CFD) analysis campaign was conducted to evaluate the performance of using spark plugs to assist gasoline compression ignition (GCI) combustion during cold idle operations. A conventional spark plug using single-sided J-strap design was put at a location on the cylinder head to facilitate spray-guided spark assistance. Ignition was modeled with an L-type energy distribution to depict the breakdown and the arc-to-glow phases during the energy discharge process. Several key design parameters were investigated, including injector clocking, number of nozzle holes, spray inclusion angle, number of fuel injections, fuel split ratio, and fuel injection timings. The study emphasized the region around the spark gap, focusing on flame kernel formation and development and local equivalence ratio distribution. Flame kernel development and the ignition process were found to correlate strongly with the fuel stratification and the flow velocity near the spark gap. The analysis results showed that the flame kernel development followed the direction of the local flow field. In addition, the local fuel stratification notably influenced early-stage flame kernel development due to varying injection spray patterns and the fuel injection strategies. Among these design parameters, the number of nozzle holes and fuel injection timing had the most significant effects on the engine combustion performance.

Investigation into ethanol effects on combustion and particle number emissions in a spark-ignition to compression-ignition (SICI) engine

Spark assistance along with oxygenated components addition is a promising method to achieve stable compression ignition, high thermal efficiency and low particle emission. To this end, ethanol blended with non-oxygenated gasoline was fueled to an engine working with spark-ignition to compression-ignition (SICI) mode under air dilution and exhaust-diluted conditions. The effects of ethanol addition on engine performance including combustion characteristics, fuel economy, particle number (PN) emissions, were studied in two categories: changing research octane number (RON) by varying ethanol content and maintaining RON by changing fuel type. The results showed that ethanol addition by splash blending suppressed knock tendency, and the knock intensity could be lowered by up to 65–75% with increasing ethanol content. However, when maintaining the same RON, the ethanol-gasoline blend exhibited higher knock intensity than pure gasoline due to synergistic effects between ethanol and aromatics on auto-ignition. Compared to pure spark ignition with high-RON gasolines, using ethanol-gasoline blends under SICI could reduce the minimum fuel consumption rate by up to 25 g/(kW·h). To characterize the high-efficiency cycles under SICI, two dimensionless parameters were proposed by considering the ratios of heat release amount and duration between the flame propagation stage and auto-ignition stage. The two parameters showed good exponential correlation. As for emissions, blending ethanol could basically reduce PN emissions under SICI mode except for the cases with significant increase in nucleation particles, such as those with high knock intensity under stoichiometric condition and poor combustion quality under heavily exhaust-diluted conditions. The total PN reduction by blending ethanol is mainly due to the decrease of accumulation mode particles, during the stage of flame propagation rather than auto-ignition. Blending ethanol into non-oxygenated gasoline will directly increase unburned hydrocarbons and nitrogen oxides due to the low auto-ignition propensity of ethanol under stoichiometric or moderately lean conditions according to the temperature-pressure trajectory. Therefore, a dedicated combustion system with higher compression ratio and lean-boosted mixture is required to enhance ethanol's reactivity and achieve better fuel economy along with low PN emission for diluted SICI combustion.

Investigation into pressure dependence of flame speed for fuels with low and high octane sensitivity through blending ethanol

Spark assistance for homogeneous charge compression ignition (HCCI) can control combustion phasing, improve thermal efficiency, and reduce emissions in gasoline engines. As the characteristics of flame propagation determine the control authority of ignition timing, it is important and necessary to investigate pressure dependence of flame speed in the lean-premixed mixture relative to engine operating conditions. Experimental study in an optical rapid compression machine (RCM) and simulation work were carried out using two fuels comprising n-heptane/iso-octane/ethanol with varied octane sensitivity (S). The effective pressure ranged from 10 to 35 bar, temperature from 715 to 860 K, and equivalence ratios between 0.3 and 0.7 to cover the region of lean flammability limits of low and high S fuels with ethanol blended. Based on pressure profiles, flame speed extracted from images, and sensitivity analysis of flame speed, the dependence of flame speed on the effective pressure in low and high S fuels was discovered and the fundamental mechanism behind this phenomena became to be understood in the negative temperature coefficient (NTC) and non-NTC regions, respectively. In the studied temperature conditions, the flame speed of high S fuel has stronger dependence on the pressure than that of low S fuel does. In the NTC region, this phenomenon is attributed to the dependence of H radical concentration on pressure in the unburned mixture and flame structure. In the non-NTC region, promoting effect of dominant reactions varied with pressure can significantly influence pressure dependence of flame speed. Although quite limited data of laminar burning velocity for studied fuels were obtained in high pressures (>15 bar), the trend of flame speed's dependence on pressure was well predicted by two models with different but well-accepted core mechanisms, showing consistent results with the experimental ones in the RCM.

Effect of octane number and thermodynamic conditions on combustion process of spark ignition to compression ignition through a rapid compression machine

Spark assistance in homogeneous charge compression ignition (HCCI) is a promising method to improve combustion stability. Fundamental experiments were carried out in a rapid compression machine along with chemical kinetics analysis to investigate the complete combustion process of spark ignition to compression ignition (SICI) using ethanol-blended fuels. Five fuels, consisting of n-heptane, iso-octane and ethanol with different fractions, are divided into two groups. The fuels with different research octane number (RON) and motor octane number (MON) but identical octane sensitivity (S) are in the same group. The equivalence ratio is fixed at 0.5, and the experimental pressure covers the engine-relevant conditions (10–35 bar) while the target temperature ranges from 735 K to 860 K, overlapping most regions with negative temperature coefficient (NTC) of n-heptane and iso-octane. Results show that octane sensitivity with low RON has poor ability to evaluate fuel reactivity especially in the vicinity of “beyond MON” area due to low-temperature oxidation acceleration of ethanol. The influence of fuel reactivity, auto-ignition heat release amount and flame compression effect on knock intensity enhancement decreases in turn. The lower transition temperature and pressure at the time of auto-ignition is observed in the fuel with lower RON regardless of S, resulted from stronger LTHR and greater temperature rise from cool flame. The fuel with medium RON and S based on ethanol blending is more suitable for SICI combustion since it can make a better balance among knock intensity, dilution tolerance and control authority from flame in the conditions studied, which gives an insight into the effect of ethanol blends on combustion process and provides a reference for fuel design aimed at lean SICI combustion.

Impact of octane sensitivity and thermodynamic conditions on combustion process of spark-ignition to compression-ignition through an optical rapid compression machine

Spark assistance is an effective method to improve combustion stability of homogeneous charge compression ignition (HCCI) with lean mixture. Ethanol, a renewable energy, blended with commercial fuels is a promising method to deal with problems of energy safety and greenhouse gas (GHG) emission. However, the influence of ethanol blends on spark ignition to compression ignition is not clear. To this end, this study presents experimentally fundamental investigation on the compression ignition (with and without spark assistance) of ethanol-blended gasoline surrogate fuel in an optical rapid compression machine at the equivalence ratio of 0.5. Three fuels with different octane sensitivities (S) comprising n-heptane/iso-octane/ethanol were formulated and S is the difference between research octane number (RON) and motor octane number (MON). Effective temperature of experiments ranges from 730 K to 860 K, overlapping most of the temperature region with negative temperature coefficient (NTC) of iso-octane at the corresponding equivalence ratio, and the pressure is consistence with engine-relevant operating conditions. The results show that more fuel reactivity of ethanol than iso-octane at 860 K is not attributed to the NTC behavior of iso-octane but to the reactive species generation in ethanol oxidation. There is always a positive correlation between effective pressure and knock intensity (KI). At lower temperature (<785 K), higher S results in the lower KI, while at higher temperature (860 K), the heat amount released by auto-ignition instead of S has a dominant impact on KI. Moreover, buffer gas dilution tolerance is not merely affected by laminar speed itself but determined by the intensity of heat release ahead of auto-ignition. The intensity of these heat release is proportional to flame speed and lower heating value (LHV). High S fuel is more sensitive to extra dilution at a fixed thermodynamic condition due to lower energy content, while the overall ignition delay (OID) requirement of no auto-ignition in the end gas is similar reflecting certain independence of fuel type. Medium S fuel has the better relationship between the timescale of flame propagation and auto-ignition, which is more suitable for spark-ignition to compression-ignition (SICI). This investigation provides a reference to fuel design for real engine applications.

Improvement in the combustion mode transition for a spark ignition engine capable of homogeneous charge compression ignition

It is fairly challenging to achieve a smooth mode transition between spark ignition combustion and homogeneous charge compression ignition combustion for a spark ignition engine capable of homogeneous charge compression ignition, because their in-cylinder thermal and charge mixture properties are quite different owing to the distinct combustion characteristics. In this paper, a mode transition strategy between spark ignition combustion and homogeneous charge compression ignition combustion was developed over the entire transition boundary between the spark ignition mode and the homogeneous charge compression ignition mode, where the engine speed is between 1100 r/min and 2000 r/min and the corresponding load (the indicated mean effective pressure) is between 3.8 bar and 5.0 bar. During the combustion mode transition and steady-state homogeneous charge compression ignition operation the normalized air-to-fuel ratio of the engine was maintained between 1.0 and 1.3; the charge air was heated by a manifold charge cooler heated by the engine coolant, and a test gasoline fuel with a research octane number of 85 was used for all the experiments conducted. The mode transition strategy was experimentally validated on a spark ignition engine capable of homogeneous charge compression ignition equipped with electric variable-valve-timing systems, dual-lift valves and an electronic throttle control system. Because of the limitation on the electric variable-valve-timing response time, it takes 5–10 cycles of the engine, depending on the engine speed, to complete the mode transition. The throttle was opened step by step to its wide-open position for the transition from spark ignition to homogeneous charge compression ignition or closed directly to the target position for the transition from homogeneous charge compression ignition to spark ignition, where the hybrid combustion mode was employed with spark assistance to change gradually to the desired homogeneous charge compression ignition mode or spark ignition combustion mode respectively, by increasing or decreasing the percentage of homogeneous charge compression ignition combustion during the hybrid combustion operation. The experimental results show that the developed strategy is able to achieve a smooth combustion mode transition with the net mean effective pressure and the combustion phase fluctuations at the level of stable spark ignition and homogeneous charge compression ignition combustion.

Impact of Spark Assistance and Multiple Injections on Gasoline PPC Light Load

Impact of Spark Assistance and Multiple Injections on Gasoline PPC Light Load

Performance and engine-out emissions evaluation of the double injection strategy applied to the gasoline partially premixed compression ignition spark assisted combustion concept

Spark assistance has been found to improve combustion control when combined with both single and double injection operation applied to compression ignition (CI) engines using gasoline as the fuel. Previous work has verified the potential of a double injection strategy when applied to the gasoline spark assisted partially premixed compression ignition combustion (PPC) concept. The current research presents performance and engine-out emissions results using a double injection strategy with the spark assisted PPC concept and shows its benefits compared to a single injection strategy. For this purpose, a parametric study was carried out using gasoline in a high-speed single-cylinder diesel engine equipped with a modified cylinder head, which included a spark plug. The parameters that were varied during the double injection testing included: injection timing, dwell, fuel mass split between the injections and intake oxygen concentration. A detailed analysis of the air/fuel mixing process was also conducted by means of a 1-D in-house spray model (DICOM).

Conceptual model description of the double injection strategy applied to the gasoline partially premixed compression ignition combustion concept with spark assistance

New combustion concepts applied to compression ignition engines are focused on achieve low temperature combustion together with a lean mixture distribution by allowing extra time from the end of injection to the start of combustion. Recently, the use of gasoline in a compression ignition engine under PPC conditions has been demonstrated as a suitable technique to achieve this extra mixing time, however the concept has also demonstrated difficulties under low load conditions using gasoline with octane number up to 95. The use of spark assistance with single injection operation has been found to be an appropriate way to improve the combustion control, providing both temporal and spatial control over the combustion process.The current paper details the influence of the double injection strategy on the spark assisted partially premixed combustion concept compared with the single injection strategy. For this purpose, a reference combustion cycle for both injection strategies is compared in terms of the main parameters derived from the in-cylinder pressure signal as well as OH* and natural luminosity images acquired from the single-cylinder transparent engine. The cylinder head used along the research has been modified including a spark plug. In addition, a detailed analysis of the air/fuel mixing process has been developed by means of a 1-D in-house spray model.

An investigation of partially premixed compression ignition combustion using gasoline and spark assistance

Nowadays the automotive scientific community and companies are focusing part of their efforts on the investigation of new combustion modes in Compression Ignition (CI) engines, mainly based on the use of locally lean air–fuel mixtures. This characteristic, combined with exhaust gas recirculation, provides low combustion temperatures that reduce pollutant formation. However these combustion concepts have some shortcomings, related to combustion phasing control and combustion stability under the light load engine operating range which must be overcome. The aim of this work is focused on the study of the integration of phasing and cycle-to-cycle repeatability control by means of an ignition spark plug system in a CI engine working under partially premixed charge (PPC) in order to overcome the lack of combustion stability in light load conditions when very low fuel reactivity is used. To achieve this objective, experimental tests have been carried out in a single cylinder optical engine combining broadband luminosity images with cylinder pressure derived heat release rate analysis. Research results reveals the spark assistance as a proper methodology to provide temporal and spatial control over the combustion process solving the lack of cycle to cycle control on the highly premixed compression ignition modes overall in light loads with high octane number (ON) fuels. Additionally, different stages have been identified in the combustion mode. The process starts with the spark discharge, which produces a flame kernel around the spark plug that later evolves to a premixed flame front. This premixed flame front heats unburned mixture and progresses into an auto-ignition combustion that burns out the rest of the charge with higher light intensity and finally an extinction of combustion process. Finally, the effect of injected fuel mass on the combustion mode has been also tested. An increase in the injected fuel mass has a positive effect on the assistance of the spark in the combustion process for both, combustion stability and cycle to cycle control.

Excellent electrochemical performance of graphene-silver nanoparticle hybrids prepared using a microwave spark assistance process

A simple method is described for the synthesis of graphene-silver nanoparticle hybrids from graphite and silver precursors using microwave spark ignition process. Adding ecofriendly free radical initiators, in the presence of hydrogen peroxide solution leads to the expansion of graphite to graphene nanosheets. Simultaneously, silver ions intercalated between the graphene layers are reduced to silver nanocrystals leading to the development of graphene-silver nanoparticle hybrids. Transmission electron microscopic (TEM) studies reveal the successful formation of graphene-silver nanoparticle hybrids. X-ray diffraction (XRD) shows that the silver nanoparticles formed on the graphene surfaces are face centered cubic crystals. The surface composition and functional groups present on the graphene-silver nanoparticle hybrids are corroborated using X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FT-IR). The lithium storage capacity of the synthesized material, when used as an anode material for rechargeable lithium secondary batteries is investigated. Its first specific discharge capacity is observed to be 580mAhg−1 and this has been increased to 827mAhg−1, by incorporating the silver nanoparticles between the graphene platelets. The reversible capacity of the graphene-silver nanoparticle hybrids is observed to be 714mAhg−1, which is significantly higher compared to that of graphene (420mAhg−1) prepared by the same process.

Production of High‐Quality Carbon Nanoscrolls with Microwave Spark Assistance in Liquid Nitrogen

A simple method to fabricate high quality carbon nanoscrolls (CNSs) by exfoliation of natural flake graphite with the assistance of microwave sparks in liquid nitrogen is demonstrated. Field-effect transistors based on the CNSs show stable ambipolar behavior in both air and nitrogen, with maximum p-type and n-type mobilities in nitrogen of up to 3117 cm2 V−1 s−1 and 4595 cm2 V−1 s−1, respectively.

Effect of Spark Assistance on Autoignition Combustion in a Small Two-Stroke Engine

The local thermal energy of the in-cylinder mixture before combustion is critical to enable autoignition (AI) to occur in a gasoline engine. When the thermal energy is insufficient, AI combustion may become very unstable and misfire may occur. Spark assistance has been proposed as a cost-effective and convenient way to enhance the local thermal energy to reach the level required for AI. It also has the potential to make AI temporally controllable. In the work reported in this paper, spark-assisted AI was experimentally investigated on a 160 cm3 two-stroke engine. The spark assistance and internal exhaust gas recirculation were jointly applied to achieve and control AI. The results showed that, at higher engine loads, the spark timing had a significant effect on AI combustion. The timing of the AI was advanced with advanced spark timing. The peak cylinder pressure and heat release rate increased with advanced spark timing. However, the combustion duration was quite independent of the spark timing. At lower engine loads, the spark assistance significantly reduced the cyclic variation in AI combustion. At a fixed engine operating condition with a light load, the spark assistance was only effective when the spark timing is sufficiently advanced. The advancement of the spark timing required to make the spark assistance effective may vary with the engine load and the air-to-fuel ratio.

Project Omnivore: A Variable Compression Ratio ATAC 2-Stroke Engine for Ultra-Wide-Range HCCI Operation on a Variety of Fuels

The paper describes the principal features of Omnivore, a spark-ignition-based research engine designed to investigate the possibility of true wide-range HCCI operation on a variety of fossil and renewable liquid fuels. The engine project is part-funded jointly by the United Kingdom's Department for the Environment, Food and Rural Affairs (DEFRA) and the Department of the Environment of Northern Ireland (DoENI). The engineering team includes Lotus Engineering, Jaguar Cars, Orbital Corporation and Queen's University Belfast. The research engine so far constructed is of a typical automotive cylinder capacity and operates on an externally scavenged version of the two-port Day 2-stroke cycle, utilising both a variable charge trapping mechanism to control both trapped charge and residual concentration and a wide-range variable compression ratio (VCR) mechanism in the cylinder head. This approach permits individual control of retained and compression heat as separate inputs to the ATAC combustion process (now commonly referred to as HCCI), an ideal situation which is not possible when attempting to operate a traditional fixed compression ratio, variable valve timing 4-stroke engine in HCCI combustion. The ease of application of the VCR system due to the elimination of poppet valves for gas exchange is fundamental to the concept and this feature is discussed in detail, together with the very wide range of compression ratios that the chosen solution permits (from 10:1 to 40:1 in this initial configuration). In addition to describing the engine and its technologies, test results from its initial operation on 98 RON gasoline are presented, including stable operation at idle load and 450 rpm in true HCCI (i.e. without spark assistance).

Cylinder-to-Cylinder Variations in a V6 Gasoline Direct Injection HCCI Engine

Despite the fact that homogeneous charge compression ignition (HCCI) has been demonstrated as a combustion technology feasible for implementation with different fuels in various types of engines, cylinder-to-cylinder variations (CTCVs) in multicylinder HCCI engines remain one of the technical obstacles to overcome. A reduction in CTCV requires further developments in control technology. This study has been carried out with regard to the overall engine parameters, involving geometric differences between individual cylinders, coolant paths through the engine, combustion chamber deposits, and also the differences in the inlet temperature distributions between the cylinders. Experimental investigations on the Jaguar V6 HCCI research engine with negative valve overlapping and cam profile switching show that the differences in the rate of pressure rise between the cylinders can be larger than 1 bar/CA deg and that the load differences can be as high as 5–10%. It has been found that some individual cylinders will approach the misfiring limit far earlier than the others. The complex interaction between a number of parameters makes the control of the multicylinder engine a serious challenge. In order to avoid these differences, an active cylinder balancing strategy will be required. It has been observed that spark assistance and split injection strategy deliver the best control for the cylinder balance. However, spark assistance is restricted to low loads and low engine speeds, while split injection requires a considerable effort to optimize its possible settings. This paper defines the most important parameters influencing cylinder-to-cylinder variations in the HCCI engine and aims to put forward suggestions that can help to minimize the effect of cylinder-to-cylinder variations on the overall engine performance.

Grinding of cemented carbide with electrical spark assistance

The paper presents the behaviour of WC–TiC–(TaNb)C–Co cemented carbide whilst diamond grinding with electrical spark discharges incorporated at the wheel–work interface. The effect of the current and the pulse on-time of the discharges on the material removal rate and grinding forces is studied to elucidate the mechanism of material removal. The results indicate that the discharges enhance the grinding performance by effectively declogging the wheel surface. The increase in the wear resistance of the material at low discharge power is interpreted in terms of the role of fracture toughness in the wear of the composite.