Jaeheun Kim

Effects of water direct injection on the torque enhancement and fuel consumption reduction of a gasoline engine under high-load conditions

Water was directly injected into the cylinder with an injection pressure of 5 MPa to investigate its effect on engine performance and emissions in a gasoline engine. The test engine was a 1.6-L naturally aspirated prototype engine consisted of water direct injection and port fuel injection systems. The engine featured a compression ratio of 13.5. Commercial gasoline direct injection injectors were used to inject the water. The water was injected at a fixed timing of −120 crank angle degrees after top dead center. The addition of water showed potential to mitigate the knock occurrence at part-load condition where the knock initially started to occur due to the high compression ratio. It allowed a further advance of spark timing; thus, the brake-specific fuel consumption was improved. The effects of water injection were further investigated under full-load condition within the engine speed range of 1500–3000 r/min. The water effectively reduced the in-cylinder temperature and the exhaust gas temperature; therefore, charge cooling through over-fueling (fuel enrichment) was eliminated with reduced brake-specific fuel consumption. Increase in the injected water mass resulted in further spark advance without the knock occurrence and provided room for further brake-specific fuel consumption reduction. An optimum water mass existed because too much water deteriorated the combustion efficiency, burn duration, and cycle efficiency. The positive effects of water injection were dulled with increased engine speed because the knocking resistance was already high intrinsically with the higher engine speed.

Effect of the air-conditioning system on the fuel economy in a gasoline engine vehicle

The air-conditioning system is the single largest auxiliary load on a vehicle. This implies that the air-conditioning system is the key component among all accessories which causes the fuel economy to deteriorate. Therefore, it is important to verify the primary parameters of the components of the air-conditioning system which affect the fuel consumption. This paper presents the effect of each component of the air-conditioning system on the fuel consumption of a conventional gasoline engine vehicle operating at various engine speeds. It was found that air-conditioning operation increased the fuel consumption by 90% maximum compared with the operation without air-conditioning during the idling condition. As the vehicle speed increased, the portion of the fuel consumption due to the compressor of the air-conditioning system increased, while the portion of the fuel consumption due to the alternator decreased. Other components such as the blower, the cooling fan and the clutch maintained nearly constant portions of the torque distribution from the alternator irrespective of the vehicle speed.

An Investigation on the Effects of Late Intake Valve Closing and Exhaust Gas Recirculation in a Single-Cylinder Research Diesel Engine in the Low-Load Condition

The effects of late intake valve closing and exhaust gas recirculation on the emissions and the engine performance of a single-cylinder diesel research engine were observed. Two cam profiles (symmetric and asymmetric) were implemented using an offset angle at various intake valve closing timings to characterize the engine performance and the emissions. The injection timings were swept at every condition to evaluate the optimal operating conditions. The highest indicated mean effective pressure was observed once the combustion phasing was tuned to the optimum crank angle (in degrees) by varying the injection timing. The indicated mean effective pressure exhibited a slight penalty when both exhaust gas recirculation and late intake valve closing were used in comparison with the base intake valve closing timing with no exhaust gas recirculation. However, an appropriate combination of the exhaust gas recirculation with late intake valve closing was effective in reducing the nitrogen oxide emissions owing to the decreased in-cylinder temperature. The prolonged ignition delay with exhaust gas recirculation and late intake valve closing also contributed to the improvement in the nitrogen oxides–smoke trade-off relationship. The potential for further reduction in the smoke emissions with the asymmetric cam profile was observed. An increase in the in-cylinder swirl motion was expected, which enhanced the air–fuel mixing process.

The effects of late intake valve closing and different cam profiles on the in-cylinder flow field and the combustion characteristics of a compression ignition engine:

The effects of the late-intake-valve-closing strategy and the different types of cam profile were observed in a single-cylinder compression ignition research engine. Experiments were carried out with two engine loads in naturally aspirated conditions. The late-intake-valve-closing strategy exhibited an improvement in the conventional trade-off between the nitrogen oxide emissions and the smoke emissions, as stated in other relevant work. However, it was found to be effective only for the premise that a sufficiently high mass of oxygen is trapped inside the cylinder, which ensured that the smoke emissions did not deteriorate with exhaust gas recirculation. This improvement in the trade-off decreased when the global air excess ratio inside the cylinder reached close to unity. The major disadvantages of the late-intake-valve-closing strategy included deterioration in the indicated mean effective pressure and the reduced mass of oxygen trapped inside the cylinder. The decrease in the indicated mean effective pressure was attributed to the reduction in the effective compression ratio followed by the reduction in the thermal efficiency in terms of the thermodynamics. The volumetric efficiency decreased owing to the backflow of the in-cylinder charge into the intake manifold. This implied that intake boosting was necessary not only to recover the efficiency to the original level but also to extend the engine load with a sufficient amount of air. The manipulation of cam profiles yielded further improvement in the trade-off relationship between the nitrogen oxide emissions and the smoke emissions. The flow field measurements obtained using particle image velocimetry and direct imaging of the combustion of the fuel spray demonstrated that the asymmetric cam profile effectively increased the swirl ratio inside the cylinder. Further improvement in the trade-off relationship between the nitrogen oxide emissions and the smoke emissions was realized because of this increased swirl intensity, which provided a better environment for air utilization. The smoke emissions were suppressed without a significant increase in the nitrogen oxide emissions.

Emission reduction through internal and low-pressure loop exhaust gas recirculation configuration with negative valve overlap and late intake valve closing strategy in a compression ignition engine

An investigation was carried out to examine the feasibility of replacing the conventional high-pressure loop/low-pressure loop exhaust gas recirculation with a combination of internal and low-pressure loop exhaust gas recirculation. The main objective of this alternative exhaust gas recirculation path configuration is to extend the limits of the late intake valve closing strategy, without the concern of backpressure caused by the high-pressure loop exhaust gas recirculation. The late intake valve closing strategy improved the conventional trade-off relation between nitrogen oxides and smoke emissions. The gross indicated mean effective pressure was maintained at a similar level, as long as the intake boosting pressure kept changing with respect to the intake valve closing timing. Applying the high-pressure loop exhaust gas recirculation in the boosted conditions yielded concern of the exhaust backpressure increase. The presence of high-pressure loop exhaust gas recirculation limited further intake valve closing retardation when the negative effect of increased pumping work cancelled out the positive effect of improving the emissions’ trade-off. Replacing high-pressure loop exhaust gas recirculation with internal exhaust gas recirculation reduced the burden of such exhaust backpressure and the pumping loss. However, a simple feasibility analysis indicated that a high-efficiency turbocharger was required to make the pumping work close to zero. The internal exhaust gas recirculation strategy was able to control the nitrogen oxides emissions at a low level with much lower O2 concentration, even though the initial in-cylinder temperature was high due to hot residual gas. Retardation of intake valve closing timing and intake boosting contributed to increasing the charge density; therefore, the smoke emission reduced due to the higher air–fuel ratio value exceeding 25. The combination of internal and low pressure loop loop exhaust gas recirculation with late intake valve closing strategy exhibited an improvement on the trade-off relation between nitrogen oxides and smoke emissions, while maintaining the gross indicated mean effective pressure at a comparable level with that of the high-pressure loop exhaust gas recirculation configuration.

Spray and Combustion Characteristics of n-dodecane in a Constant Volume Combustion Chamber for ECN Research

The spray and combustion characteristics of n-dodecane fuel were investigated in a CVCC (constant volume combustion chamber). The selection of ambient conditions for the spray followed ECN (engine combustion network) guidelines, which simulates the ambient condition of diesel engines at start of fuel injection. ECN is a collaboration network whose main objective is to establish an internet library of well-documented experiments that are appropriate for model validation and the advancement of scientific understanding of combustion at conditions specific to engines. Therefore repeatability of the experiments with high accuracy was important. The ambient temperature was varied from 750 to 930 K while the density was fixed at around 23 kg/m. The injection pressure of the fuel was varied from 500 to 1500 bar. The spray was injected in both non-reacting (O2 concentration of 0%) and reacting conditions (O2 concentration of 15%) to examine the spray and the combustion characteristics. Direct imaging with Mie Scattering was used to obtain the liquid penetration length. Shadowgraph was implemented to observe vapor length and lift-off length at non-reacting and reacting conditions, respectively. Pressure data was analyzed to determine the ignition delay with respect to the spray and ambient conditions.

The Effects of Intake Valve Closing Timing on Engine Performance and Emissions in a DME Compression Ignition Engine at Low Load Cold Start Condition

The effective compression ratio reduction by means of late intake valve closing (LIVC) strategy was applied in a di-methyl ether (DME) compression ignition engine to investigate its potential effects on the engine performance and emission at cold start condition. The single injection timing of the DME was varied from the beginning to the end of compression stroke. The DME was injected directly into the cylinder with an injection pressure of 60 MPa. The indicated mean effective pressure (IMEP), heat release rate and combustion duration was investigated at two different intake valve closing (IVC) conditions—base IVC of 28 degree after bottom dead center (ABDC) and LIVC of 43.9 degree ABDC. The other experimental conditions such as injection duration and the environmental temperature remained fixed. The IMEP characteristics with respect to injection timings of two different IVC timing showed similar trend at conventional combustion regime. The IMEP distribution was shifted towards advanced injection timing direction for LIVC condition. In other words, the injection timing of LIVC condition had to be advanced compared to that of base IVC timing in order to produce equal power output. The reduction in the compression ratio had resulted in lower compression pressure and the temperature, so the ignition delay was increased and the overall heat release rate was retarded to retarded crank angle. However, the combustion characteristics in terms of combustion duration and the heat release rate curve did not show great differences at early injection timings (earlier than −30 crank angle degrees ATDC (after top dead center)). The NOx emission was reduced by around 10 % due to the reduced effective compression ratio. The prolonged ignition delay which enhanced the mixture homogeneity was also considered to have contributed on the reduction of NOx emission. The HC and CO emissions of LIVC condition were relatively higher than those of base IVC condition due to the lowered in-cylinder temperature. The smoke formation was low due to the intrinsic properties of DME. The exhaust gas temperature was higher for the LIVC timing condition. The expelled portion of the charge during the compression resulted in lower heat capacity of the working gas. The in-cylinder gas temperature increased more when the same amount of fuel energy input was delivered to the gas with lower heat capacity. It was found that, malfunction of the piezo injector occurred when applying DME fuel with inappropriate setup. It was assumed that the vaporization of the DME might occur inside the injector when the engine coolant temperature increased. The movement of the piezo stack was not able to be translated into injection events due to the gas phase inside the injector. The fuel injector was restored and able to maneuver with the injection events again when the fuel return line was pressured above the vapor pressure. In future, further experiments need to be carried out at fully warmed-up condition in order to reveal its potential of reducing effective compression ratio on improving engine performance.