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Computational Fluid Dynamics (CFD) simulations are performed to study the potential of Energy-Assisted Compression Ignition (EACI) strategy for enabling ignition and enhancing combustion of different cetane number jet fuels during high-altitude operation. EACI employs an ignition assistant (IA), which is an advanced glow-plug design with the ability to sustain higher temperatures for prolonged periods, to provide the necessary ignition energy for precise ignition control and enhanced combustion. In the numerical simulations, the combustion chemistry solver is coupled with a multi-component wide distillation fuel mechanism, energy source modeling, and a turbulence-chemistry interaction model to accurately capture the Ignition Assisted-combustion. The simulation is first validated against optical engine measurements for CN 48 jet fuel and then transferred to another single-cylinder test engine to study the ignition and combustion characteristics of EACI with CN 35 jet fuel at varying IA temperatures. Simulation results show that EACI significantly improves fuel ignitability. Ignition delay reductions for CN 48 fuel of 57% and CN 35 fuel of 25% are noted at IA temperatures of 1550 K and 1405 K compared to when the IA is switched off. Furthermore, EACI improved the combustion efficiency to 99.7% compared to the 90% estimated for the IA off case in the optical engine.

This study investigates the use of a commercial-off-the-shelf (COTS) ceramic glow-plug to assist ignition of jet fuel blends with cetane numbers of 30 and 35, below the minimum cetane number of 40 for #2 diesel. Experiments were carried out on a single-cylinder compression-ignition engine operating at 1200 RPM for single and dual-injection (pilot + main) timing sweeps. The COTS glow-plug, termed the ignition assistant, was operated at varying input power levels between 0 and 70 W (stock maximum power input is 30 W) at each SOI. Results demonstrate that the use of an ignition assistant at the higher input powers (50 and 70 W) enables operation over a wider range of SOI timings where more advanced times are limited by high pressure-rise rates and more retarded times are limited by rapidly increasing coefficient of variation of gross indicated mean effective pressure. Use of the ignition assistant enables stable combustion at later injection timings increasing the operable range of SOI timings. For the CN 30 fuel, at earlier injection timings, pressure traces, and heat release analysis demonstrated the advancement of start of combustion and combustion phasing with the ignition assistant on. At retarded injection timings where combustion would not otherwise occur completely for the CN 30 fuel, operating the ignition assistant at the higher powers enabled combustion phasing to be advanced and combustion to be stabilized at conditions where, with the ignition assistant off, misfire (flameout) would occur. Furthermore, the ignition assistant enabled combustion phasing to follow an approximately linear response with respect to SOI timing over a wider range of SOI times.

Water injection has been used to reduce the charge temperature and mitigate knocking due to its higher latent heat of vaporization compared to gasoline fuel. When water is injected into the intake manifold or into the cylinder, it evaporates by absorbing heat energy from the surrounding and results in charge cooling. However, the effect of detailed evaporation process on the combustion characteristics under gasoline direct injection relevant conditions still needs to be investigated. Therefore, spray study was firstly conducted using a multi-hole injector by injecting pure water and water-methanol mixture into constant volume combustion chamber (CVCC) at naturally aspirated and boosted engine conditions. The target water-fuel ratio was fixed at 0.5. Mie-scattering and schlieren images of sprays were analyzed to study spray characteristics, and evaluate the amount of water vaporization. The qualitative analysis of the water and water-methanol sprays demonstrated the inability of water to evaporate completely. Moreover, simulations of water spray injection were also performed under the framework of CONVERGE using the Eulerian-Lagrangian modeling approach. The amount of vaporized water, evaporation rate, temperature evolution, saturation ratio was analyzed and compared under different crank angles. The presented simulation scheme will provide informative support for the future design of water injection pattern in internal combustion engines.

In this study, the effect of elevated fuel temperatures on the spray characteristics of gasoline-ethanol blends were studied in an optically accessible constant volume spray and combustion vessel. MAHLE SmartHeat® is a fuel heater located directly upstream of the fuel injector. High speed images of the spray injected from a six-hole gasoline direct injection injector typical of a side-injection engine were captured with shadowgraph imaging technique. Two fuel blends, gasoline with 10% ethanol (E10) and 85% ethanol (E85) were investigated at ambient conditions of 1 bar, 45°C and 4 bar, 180°C respectively at an injection pressure of 100 bar. Fuel temperatures were varied from 75 to 250°C. A comparison of the near nozzle and the global spray characteristics was made for the two fuels at those temperatures. Results showed that flash boiling leads to two primary effects for the two fuel blends: (i) an appreciable increase in spray angle near the exit of the nozzle followed by (ii) a decrease in spray angle downstream of the nozzle due to the interaction of the plumes and the collapsing of the spray. Furthermore, for both fuel blends, upon flash boiling, entrainment and mixing were reduced downstream of the nozzle because of the collapse of the spray. To reduce this effect, nozzle orientations and geometries should be modified.

Natural gas has a higher knock suppression effect than gasoline which makes it possible to operate at higher compression ratio and higher loads resulting in increased thermal efficiency in a spark ignition engine However, using port fuel injected natural gas instead of gasoline reduces the volumetric efficiency from the standpoints of the charge displacement of the gaseous fuel and the charge cooling that occurs from liquid fuels. This article investigates the combustion and engine performance characteristics by utilizing experimental and simulation methods varying the natural gas-gasoline blending ratio at constant engine speed, load, and knock level. The experimental tests were conducted on a single cylinder prototype spark ignited engine equipped with two fuel systems: (i) a Direct Injection system for gasoline and (ii) a Port Fuel Injection (PFI) system for compressed natural gas. For the fuels, gasoline with 10% ethanol by volume (commercially known as E10) with a research octane number of 91.7 is used for gasoline via the DI system, while methane is injected through PFI system. The knock suppression tests were conducted at 1500 rpm, 12 bar net indicated mean effective pressure wherein the engine was boosted using compressed air. At 60% of blending methane with E10 gasoline, the results show high knock suppression. The net indicated specific fuel consumption is 7% lower, but the volumetric efficiency is 7% lower compared to E10 gasoline only condition. A knock prediction model was calibrated in the 1-D simulation software GT-Power by Gamma Technologies. The calibration was conducted by correlating the simulated engine knock onset with the experimental results. The simulation results show its capability to predict knock onset at various fuel blending ratios.

One of the limiting factors improving the efficiency of gasoline engines is engine knock. Various techniques including using fuels that result in charge cooling are employed to mitigate knock and improve efficiency. Water and methanol have higher heat of vaporization than gasoline. When water or methanol is injected into the intake manifold, it evaporates by exchanging energy with the charge mixture resulting in charge cooling. This allows the engine to be run with advanced spark timing without engine knock. With this motive, the impact of water - methanol injection on the engine performance of a gasoline direct injection engine was investigated. Experimental studies were conducted on a single-cylinder 0.55L engine with a compression ratio of 10.9:1 at 800 kPa net indicated mean effective pressure and 1500 revolutions per minute. Baseline tests without water injection were conducted by direct injection of gasoline fuel blended with 10% ethanol (E10). Four mixtures: 100% water, 75% water + 25% methanol, 50% water + 50% methanol and 100% methanol were used with port injection. Spark ignition timing, flow rate of the fuel and the four mixtures were varied to be within the controlled knock limit while maintaining an excess air ratio of 1.0. Comparisons on the effectiveness of these mixtures indicate that higher methanol content in the mixture helped in reaching the maximum brake torque condition at lower mixture fuel ratios. Combustion stability of the engine was improved with the addition of water and water-methanol blends due to the sensitivity of combustion phasing at advanced spark timings reducing the variation in indicated mean effective pressure. Exhaust gas temperatures decrease with the addition of water and water-methanol blends due to the combined effect of increased charge cooling and improved combustion phasing.

A common approach of high efficiency engines is to utilize high compression with late intake valve closing (LIVC) to realize an over-expanded cycle. A multi-link cranktrain can also realize an over-expanded cycle with the same geometric intake displacement as a baseline engine while extending the expansion stroke. These two types of over-expanded cycle engines and a baseline engine are investigated and compared in this simulation study. The baseline engine model is calibrated based on the experimental results from a four-cylinder, boosted, spark-ignited engine with compression ratio (CR) of 10.5:1. The CR of high compression ratio engine and multi-link over-expanded engine is 13.0:1 and 10.5:1, respectively. The over-expansion ratio of multi-link engine is 1.5. These three engines were optimized and investigated at three conditions: 1300 rpm 330 kPa net IMEPnet, 1500 rpm 1300 kPa IMEPnet, and 2500 rpm 1000 kPa IMEPnet. At 1300 rpm 330 kPa IMEPnet, multi-link over-expanded engine and high compression engine both used LIVC. With LIVC, the net indicated efficiency of the high compression engine and multi-link engine were improved by 5.2% and 2.4% (relative), respectively, compared to the same engine without LIVC. Multi-link over-expanded engine benefited from its lower knock propensity and over-expansion at medium to high load conditions. At 1500 rpm 1300 kPa IMEPnet, the net indicated efficiency of the multi-link engine was 13.7% and 14.2% (relative) higher than the high compression engine and baseline engine, respectively. At the peak brake efficiency condition of the high compression engine, the net indicated efficiency of multi-link engine was 8.6% (relative) higher than the high compression engine.

A boosted spark-ignited over-expanded engine was investigated through 1-D engine simulation. A conventional 4-stroke turbocharged spark-ignited engine with 10.5:1 compression ratio (CR) was selected as the baseline engine. The Atkinson cycle engine model was developed and calibrated based on a multi-link mechanism. The compression ratio (CR) and over expansion ratio (OER) of the Atkinson cycle engine are 10.5 and 1.5, respectively. Two speed and load conditions of 1500 rpm, 13 bar net indicated mean effective pressure (IMEPnet) and 3500 rpm, 20 bar IMEPnet with valve timing optimization were investigated. Results depict that the increase in indicated efficiency of Atkinson cycle engine was from both portions of over-expansion and non-over-expansion portion of the cycle. Atkinson cycle engine benefits from lower knock propensity and lower exhaust temperature. At 1500 rpm, 13 bar IMEPnet, the simulation results indicated that energy loss due to combustion phasing was 2.1% and 0.4% for baseline and Atkinson cycle engine. Net indicated efficiency of Atkinson cycle engine was increased by 16%. At 3500 rpm, 20 bar IMEPnet, baseline engine was operated at knock limited spark timing and fuel enrichment to reduce the turbine-inlet temperature. Net indicated efficiency of optimized Atkinson cycle engine at 3500 rpm 20 bar IMEPnet was higher by 27% in comparison to the optimized baseline engine. The combustion phasing loss was 1.2% and 0.6% for baseline and Atkinson cycle engine, respectively. The energy loss due to fuel enrichment was 6.0% and 1.6% for baseline engine and Atkinson cycle engine, respectively, indicating that the Atkinson cycle engine was beneficial to maximize its efficiency.

This paper experimentally investigates the effect of water injection in the intake manifold on a naturally aspirated, single cylinder, Gasoline Direct Injection engine to determine the combustion and emissions performance with combustion knock mitigation. The endeavor of the current study is to use water injection to attain the optimum combustion phasing without knocking. Further elevated intake air temperature tests were conducted to observe the effect of water injection with respect to combustion and emissions. Experiments were carried out at medium load condition (800 kPa NIMEP, 1500 RPM) at intake air temperatures between 30–90° C in 20° C increments. Two fuels, an 87 AKI and a 93 AKI were used in this study. Baseline tests were undertaken with the high-octane fuel (93 AKI) to achieve optimal combustion phasing corresponding to Maximum Brake Torque (MBT) without water injection. Water injection was utilized for the low octane fuel to achieve combustion phasing of 8–10° ATDC and within the controlled knock limit. Combustion phasing was achieved by controlling the ignition timing, water injection quantity and timing to the knock threshold. The results showed that water injection and the resultant charge cooling mitigates combustion knock and an optimum combustion phasing based on indicated fuel conversion efficiency is achieved with a water to fuel ratio of 0.6. Water injection reduces the NOx emissions while achieving better indicated thermal efficiency compared to the baseline tests. A detailed comparison is presented on the combustion phasing, indicated thermal efficiency, burn durations, HC, NOx and PN emissions in this paper.

Natural gas has a higher knock suppression effect than gasoline which makes it possible to operate at higher compression ratio and higher loads resulting in increased thermal efficiency in a spark ignition engine However, using port fuel injected natural gas instead of gasoline reduces the volumetric efficiency from the standpoints of the charge displacement of the gaseous fuel and the charge cooling that occurs from liquid fuels. This article investigates the combustion and engine performance characteristics by utilizing experimental and simulation methods varying the natural gas-gasoline blending ratio at constant engine speed, load, and knock level. The experimental tests were conducted on a single cylinder prototype spark ignited engine equipped with two fuel systems: (i) a Direct Injection system for gasoline and (ii) a Port Fuel Injection (PFI) system for compressed natural gas. For the fuels, gasoline with 10% ethanol by volume (commercially known as E10) with a research octane number of 91.7 is used for gasoline via the DI system, while methane is injected through PFI system. The knock suppression tests were conducted at 1500 rpm, 12 bar net indicated mean effective pressure wherein the engine was boosted using compressed air. At 60% of blending methane with E10 gasoline, the results show high knock suppression. The net indicated specific fuel consumption is 7% lower, but the volumetric efficiency is 7% lower compared to E10 gasoline only condition. A knock prediction model was calibrated in the 1-D simulation software GT-Power by Gamma Technologies. The calibration was conducted by correlating the simulated engine knock onset with the experimental results. The simulation results show its capability to predict knock onset at various fuel blending ratios.

Natural gas has a higher knock suppression effect than gasoline which makes it possible to operate at higher compression ratio and higher loads resulting in increased thermal efficiency in a spark ignition engine However, using port fuel injected natural gas instead of gasoline reduces the volumetric efficiency from the standpoints of the charge displacement of the gaseous fuel and the charge cooling that occurs from liquid fuels. This article investigates the combustion and engine performance characteristics by utilizing experimental and simulation methods varying the natural gas-gasoline blending ratio at constant engine speed, load, and knock level. The experimental tests were conducted on a single cylinder prototype spark ignited engine equipped with two fuel systems: (i) a Direct Injection system for gasoline and (ii) a Port Fuel Injection (PFI) system for compressed natural gas. For the fuels, gasoline with 10% ethanol by volume (commercially known as E10) with a research octane number of 91.7 is used for gasoline via the DI system, while methane is injected through PFI system. The knock suppression tests were conducted at 1500 rpm, 12 bar net indicated mean effective pressure wherein the engine was boosted using compressed air. At 60% of blending methane with E10 gasoline, the results show high knock suppression. The net indicated specific fuel consumption is 7% lower, but the volumetric efficiency is 7% lower compared to E10 gasoline only condition. A knock prediction model was calibrated in the 1-D simulation software GT-Power by Gamma Technologies. The calibration was conducted by correlating the simulated engine knock onset with the experimental results. The simulation results show its capability to predict knock onset at various fuel blending ratios.