Turbocharged Gasoline Direct Injection Engine Research Articles

Experimental Study of the Performance of Turbo-Charged Gasoline Direct-Injection Engine Based on Different Pre-Chamber Structures

In this paper, in order to improve the fuel economy of the actual application of the engine under multi-operating conditions, an experimental study is carried out on a turbo-charged direct-injection engine based on different pre-chamber structures. The engine used for the study is a four-cylinder turbo-charged direct-injection gasoline engine with different structures of pre-chamber spark plugs. The operating conditions in this study include load characteristics at 2000 r/min and characteristic loads at different speeds, including 3000 r/min, 3200 r/min, and 3600 r/min. With stable BMEP or fully open throttle and pedal, the experiment was conducted by the spark angle scanning method to collect data of engine power, economy, and emission under each condition. It was found that the pre-chamber structure has a direct effect on engine performance, with a clear load demarcation line for its effect. Under the WOT condition, the power of pre-chamber ignition is 1.6% higher than that of conventional spark plugs; at the low load of 2 bar, the economy of pre-chamber ignition is degraded by 6%; at the medium load of 8 bar, the economy of the two is comparable; at the large load of 16 bar, the fuel economy proves advantageous. Compared with conventional spark plugs, the pre-chamber spark angle can be advanced by 2~3 °CA, and the pre-chamber ignition with separate ground electrodes is highly reliable. The emission levels of the pre-chamber spark plugs and conventional spark plugs are comparable at all loads.

Estimation of Piston Surface Temperature During Engine Transient Operation for Emissions Reduction

Abstract Piston surface temperature is an important factor in the reduction of harmful emissions in modern gasoline direct injection (GDI) engines. In transient operation, the piston surface temperature can change rapidly, increasing the risk of fuel puddling. The prediction of the piston surface temperature can provide the means to significantly improve multiple-pulse fuel injection control strategies through the avoidance of fuel puddling. It could also be used to intelligently control the piston cooling jet (PCJ), which is common in modern engines. Considerable research has been undertaken to identify generalized engine heat transfer correlations and to predict piston and cylinder wall surface temperatures during operation. Most of these correlations require in-cylinder combustion pressure as an input, as well as the identification of numerous model parameters. These requirements render such an approach impractical. In this study, the authors have developed a thermodynamic model of piston surface temperature based on the global energy balance (GEB) methodology, which includes the effect of PCJ activation. The advantages are a simple structure and no requirement for in-cylinder pressure data, and only limited experimental tests are needed for model parameter identification. Moreover, the proposed model works well during engine transient operation, with maximum average error of 6.68% during rapid transients. A detailed identification procedure is given. This and the model performance have been demonstrated using experimental piston crown surface temperature data from a prototype 1-liter 3-cylinder turbocharged GDI engine, operated in both engine steady-state and transient conditions with an oil jet used for piston cooling turned both on and off.

Consequence of Blowby Flow and Idling Time on Oil Consumption and Particulate Emissions in Gasoline Engine

Pollutant emission standards and, in particular, those concerning particles from an internal combustion engine (ICE) are becoming increasingly restrictive. Thus, it is important to determine the main factors related to the production of particulate matter. In this article, the phenomenon of oil sweeping by the blowby gases between the rings/piston/cylinder is investigated. First, a blowby gas simulation model based on experimental results from a Turbocharged Gasoline Direct Injection (TGDI) is developed. From this model, it is possible to characterise the amount of oil swept by the blowby gases. This depends on the endgap position of both the compression and sealing rings. It also depends on the intensity of the blowby flow rate, which is highest at low rpm and high load. At 1500 rpm and full load, this flowrate exceeds 25 mg.cycle−1. From this result, it is possible to quantify the amount of oil swept by these gases as a function of the endgap position. For θrings=180°, the quantity of oil swept rises to 20 µg.cycle−1 while for θrings=30°, this decreases to 6 µg.cycle−1. The oil concentration of the blowby gas has a direct impact on the particulate emissions because the oil concentration of the backflow gas is inversely proportional to the blowby gas flowrate. As the backflow gases return to the cylinder, the oil oxidises and produces particles. Therefore, it is essential to control the oil concentration of the backflow gases. In addition, the simulation model shows the blowby flowrate becomes negative and decreases to −3.4 mg. cycle−1 in idle conditions. The amount of oil swept by the blowby is no longer directed towards the oil pan, but towards the piston crown. This phenomenon of oil storage of the piston crown in idle condition is proportional to the duration of the idle time. In order to confirm these results, experimental tests are carried out on a TGDI engine. It appears that when the idling time changes from 0 s to 7 s between two strictly identical accelerations, the level of particulate emissions is multiplied by 1.3. When the idling time changes from 0 s to 22 s between two strictly identical accelerations, the level of particulate emissions is multiplied by 3. These results confirm the mechanism of oil storage at idle highlighted by the simulation model.

Post-oxidation phenomena enhancement with scavenging and secondary air injection in exhaust manifold of a turbocharged GDI engine

A detailed investigation of post-oxidation phenomena by individual and combined effects of scavenging (VVT tuning) and secondary air injection (SAI) was performed. The 1-D simulation including a post-oxidation model developed by Stuttgart University as an international collaboration was used for investigation which includes the main exhaust gas species as CO, H2, and O2-based chemical reactions. Then, experimental validation was conducted on a 4-cylinder turbocharged gasoline direct injection (GDI) engine. From the results, it was noted that the post-oxidation can be actuated at limited operating conditions as higher overlap in moderated speed and load only when scavenging phenomena are considered. However, at lower overlap, it is restricted due to lower O2 scavenging even though the exhaust temperature meets the post-oxidation requirement. Also, the in-homogeneity observed at higher overlap that restricts the significant post-oxidation before the turbocharger upstream. On the other hand, the SAI mechanism can actuate the post-oxidation even at lower overlap if enough O2 concentration, exhaust temperature, and adequate mixing are attained. Hence, the post-oxidation zone can be extended to lower speed-load and overlap if both parameters as scavenging and SAI introduced together. This can possibly lead to better turbo-performance along with lower emissions. However, thermal efficiency needs to be compromised to some extent. It was also found that the effective post-oxidation can be actuated by SAI compared to scavenging-based phenomena if the same concentration of the O2 and temperature are maintained by both mechanisms. This appeared due to the fresh air continuously injected at the exhaust port even at the time of exhaust valve opening duration in SAI mechanism that allows the better mixing of O2 and hot unburned gas species. However, in scavenging-based phenomena, firstly, hot unburned gas passed through the exhaust manifold and then scavenged air follows which restricts mixing between scavenged air and unburned gas species.

Simulation and experimental research on the influence of lubrication on the comprehensive friction of TGDI engine

PurposeThis paper aims to investigate the effects of low-viscosity and ultralow-viscosity engine oils on the comprehensive friction and fuel economy of turbocharged gasoline direct injection (TGDI) through simulation analysis and experiments.Design/methodology/approachNumerical analysis models of friction loss for reciprocating, crankshaft and valve train are established. Based on the FAST, the friction loss of 24 specific parts of a TGDI engine was analyzed. Finally, the engine test bench was built, which was used to test the mechanical loss, external characteristics and universal characteristics.FindingsCompared with the baseline oil, lower viscosity lubricating oil can reduce the friction loss of nine components to varying degrees. When the viscosity decreases, the friction distribution ratio of reciprocating, crankshaft and balance shaft will gradually decrease. The proportion of reciprocating when using 0W12 is reduced by 4%. Tests have shown that ultralow viscosity engine oil reduces torque loss by up to 15.74% (2,000 rpm, full throttle), but its fuel consumption rate becomes higher in low-speed and high-torque conditions.Originality/valueThis work helps to understand the effect of lubricating oil characteristics on the comprehensive friction performance of the engine.

Experimental investigation of water injection and spark timing effects on combustion and emissions of a hybrid hydrogen-gasoline engine

This paper aimed to study the effects of water injection and spark timing on performance of a hybrid hydrogen-gasoline engine. For this aim, a modified four-cylinder turbocharged gasoline direct injection (GDI) engine equipped with hydrogen port injection and port water injection system was developed. In this study, the engine speed was maintained at 1300 rpm and the throttle opening of 30% with an excess air/fuel ratio of 1. The hydrogen energy percentage of 15%, water fuel mass ratio of 0.2 and 0.4 was added into the intake port. When the hydrogen energy percentage was changed, the gasoline fraction was also adjusted to keep the mixture at the stoichiometric. For all tested conditions, the spark timing was varied from 1 to 42°CA before top dead center (BTDC) with a fixed interval of 2°CA. Experimental results showed that maximum brake torque (MBT) spark timing varied when water and/or hydrogen is added. With hydrogen addition, the worsened combustion caused by water injection can be improved. Also, the variation of IMEP and COVIMEP versus spark timing became more insensitive with hydrogen addition. With water injection, the high NO emission caused by hydrogen addition can be largely reduced, however with side effect of higher HC and CO emissions.

Effect of late intake valve closing on the particle number emissions of a turbocharged gasoline direct injection engine

To achieve carbon-neutrality, efficient gasoline engines with minimal particle number emissions are being increasingly researched. In this study, the particle emission mechanism associated with late intake valve closing (LIVC) was investigated using borescopic method, and particle image velocimetry (PIV) in a 4-cylinder turbocharged gasoline direct injection engine, and a 2-cylinder optically accessible engine, respectively. The direct flame visualization of the borescope and flow visualization of the PIV measurement were used to analyze the blue flame propagation characteristics, mean in-cylinder flow velocity, and turbulent kinetic energy associated with the LIVC along with combustion analysis. The retardation of the LIVC timing reduced the particle number emissions, increased the in-cylinder flow velocity, and decreased the effective compression ratio. The improved flow velocity and reduced effective compression ratio mitigated the production of particle precursors at the expense of decelerated initial flame propagation. However, this decelerated flame propagation was compensated by the enhanced late-stage combustion generated from the increased turbulent kinetic energy of the retarded LIVC timings. The obtained results verify that the improved mixture formation and initial lower in-cylinder temperature conditions of the retarded LIVC timing reduced the particle production, which in turn enhanced the particle oxidation owing to the accelerated late-stage combustion.

Experimental investigation of particle number reduction in turbocharged GDI engines

Introduction (problem statement and relevance). Now it is difficult to imagine the automotive industry without constant improvement of the power plant. This is due to the constant tightening of environmental standards, so in environmental standards Euro 6 there is a limit of the countable concentration of particulate matters. To meet the Euro 6 environmental standard, vehicle manufacturers use catalytic converters, and gasoline particle filters (GPF). These methods of reducing the emissions of the exhaust gas are quite common, but they also have a limitation on the service life. The use of only catalytic converters and GPF may not be sufficient to meet the Euro 7 standards in the future. So, there is a need to reduce emissions with exhaust gases by improving the combustion process.The purpose of work is to investigate the combustion process of a turbocharged gasoline direct injection engine to reduce particulate matter by increasing the injection pressure and optimizing the injection timing. Methodology and research methods. The studies are of an experimental nature, the reliability of the data is confirmed by the use of modern measuring equipment and post processing of the measured data. Scientific novelty and results. The fuel injection parameters, which have a significant influence on the particulate matter formation and oxidation are defined.Practical significance. The recommendations to reduce particulate matter formation and to meet the requirements of the future Euro standards are given.

Research of Exhaust Gas Recirculation on Commercial Turbocharged Gasoline Direct Injection Engine With Intense Tumble Flow

Abstract The application of exhaust gas recirculation (EGR) technology on gasoline direct injection (GDI) engines can suppress knocking, reduce fuel consumption, and reduce NOx emissions. The effects of EGR with enhanced intake tumble flow, on the combustion phase, combustion duration, knock index and combustion cycle variation of the engine, were studied at two speeds of 1500 r/min and 2000 r/min from low to medium and to full load. The research shows that although the commercial engine has been well calibrated and optimized, the optimization of EGR and enhanced tumble flow together with the optimization of the ignition angle can improve the engine's economy and emission characteristics, while maintaining relatively fast burning speed and low combustion cycle variation. From medium to heavy load, the economy can be improved by 2.6–10%, and the minimum fuel consumption can be reduced to 213 g/kW. h. Under heavy load conditions (brake mean effective pressure (BMEP) more than 14 bars), power performance deteriorates due to insufficient boost performance. The 5–20% EGR rate brings 10% power loss. EGR combined with tumble intake has a significant effect on reducing the engine's NOx and CO, with average reductions of 60% and 22%, but HC increased by 32%.

Effects of turbocharger rotational inertia on engine and turbine performance in a turbocharged gasoline direct injection engine under transient and steady conditions

The effects of turbocharger (T/C) rotational inertia on engine and turbine performance under transient and steady engine conditions were analyzed in a 2.0 L 4-cylinder turbocharged-gasoline direct injection (T-GDI) engine. The test T/Cs consisted of heavy and light compressor wheels (C/W) and turbine wheels (T/W). The study was conducted in two research stages. First, transient engine load tests were conducted to evaluate the effect of T/C rotational inertia on transient response of the T/C, combustion performance, and fuel consumption. Seconds, steady engine load tests were conducted to find out if a light inertia T/C can run at higher efficiency under the same exhaust pulsating flow conditions within one engine cycle. In order to evaluate the engine on-board turbine instantaneous performances in the units of crank angle degree (CAD), T/C rotation speed and pressure data were measured in the experiment. The instantaneous exhaust gas mass flow rate and the temperature of upstream and downstream of the turbine were extracted by 1-D simulation. Turbine efficiency and mass flow rate parameters were calculated by combining these data. In the results, there existed positive effects of light inertia T/C on response and specific fuel consumption under transient conditions. It was also found that the light inertia T/C could show higher T/C speed fluctuation under the same exhaust pulsating flow conditions. Consequently, blade speed ratio (BSR) and turbine efficiency of light inertia T/C were partially higher than that of conventional one. However, it was not led to higher engine efficiency.

Effects of Turbocharger Rotation Inertia on Instantaneous Turbine Efficiency in a Turbocharged-Gasoline Direct Injection (T-GDI) Engine

Abstract The effects of turbocharger rotation inertia on instantaneous turbine efficiency were analyzed in a 2.0 L four-cylinder twin-scroll turbocharged gasoline direct injection (T-GDI) engine. Two turbochargers of different weights were prepared for comparison purposes: base T/C and light T/C. In order to evaluate the instantaneous efficiency of each turbocharger, a combination of engine tests and a 1D simulation was conducted. In the experiments, the instantaneous exhaust gas pressures, upstream and downstream of the turbine, were measured. The instantaneous turbocharger rotation speed was also measured. The instantaneous temperature and mass flow rate of the exhaust gas were taken from the 1D simulation results. Through a combination of measuring and simulating exhaust gas states for the turbines, the instantaneous turbine blade speed ratio (BSR), total-to-static turbine efficiency (ηts), reduced mass flow rate (φ), and reduced turbine speed (Nred) were calculated. The light T/C showed higher fluctuations in the instantaneous turbine rotation speed compared to the base T/C. This greater response from the light T/C is due to experiencing less inertia loss, this leads to higher fluctuations in the instantaneous Nred, BSR, ηts, and φ. As a result, the light T/C shows higher turbine efficiency at certain points after the start of the exhaust gas pulse cycle. This is because the greater response of the light T/C lead the operating conditions of the turbine to more efficient regions in the turbine map.

Combustion phenomena affecting particle emission under boosting conditions in a turbocharged gasoline direct injection engine

As emission regulations for vehicles have become stricter, the survival of direct injection technologies has been threatened due to increased particle emissions. By many researchers, there has been the effort to reduce the particle emissions. Nonetheless, the sources of particle emissions from turbocharged gasoline direct injection engines (T-GDI) were still not investigated enough. In this research, the particle emission from a modern turbocharged gasoline direct injection engine was investigated through combustion analysis accompanying simultaneous flame visualization. The experiments were conducted under three load conditions from naturally-aspirated to highly boosted conditions. The start of injection was swept to identify the effect of fuel mixing processes and differed combustion phenomena by the fuel injections and the boosting on engines. As results, the boosting changed the influence of heterogeneity and flow interaction by sprays, resulting differences in heat release from combustion and particle generation. The boosting on engines suppressed the agglomeration of particles into large aggregate in half, but promoted the nucleation of particles become double compared to natural aspiration. With optimized injection systems, the most impacting factors are the control of spray interaction with in-cylinder flow and oxidation processes of particles. In the boosted conditions, the uncertain particle sources could occur, such as spontaneous ignitions by mixture stratification and biased flame propagation by flow interaction. Through optimization of injection strategies, the combustion phenomena can be controlled to reduce the particle emissions in the moderate boosted conditions. The results of combustion analysis affecting the particle generation can provide the clues to reduce particle emission from T-GDI engines.

Prediction of hydrogen-added combustion process in T-GDI engine using artificial neural network

This study investigates the prediction of the combustion process using an artificial neural network (ANN), and an efficient prediction methodology is introduced. In particular, the conditions for using hydrogen as an additive to a turbo-charged gasoline direct injection (T-GDI) engine are discussed. Research to predict the physical phenomena using ANNs has been actively conducted for various applications, including internal combustion engines. However, a large amount of data must be collected under various conditions to establish these predictions. Furthermore, the prediction of complex phenomena such as engine-combustion processes mandates data collection under diverse conditions. It is therefore very costly and time-consuming to obtain these data experimentally under a wide range of conditions. However, the methodology introduced in this study can enable effective prediction of complex combustion processes, such as hydrogen-added combustion, with minimal experimental data. To implement this methodology, the target engine was modeled using commercial 1D engine-simulation software GT-Power based on certain experimental results obtained under select conditions. The data for the ANN training under an expanded range of conditions were obtained using the GT-Power engine model. According to the obtained data, the ANN model for prediction of the hydrogen-added combustion processes in the T-GDI engine was constructed, and its results were compared with the experimental results. A reasonable agreement between the compared results was observed, which demonstrated the validity and reliability of the prediction model. The constructed ANN combustion model has the potential that it can be applied to transient conditions or used as a virtual sensor, unlike general combustion models, and this study presented an economical and efficient way to build such a model.

An investigation on the effect of intake air humidification on the thermal balance of a turbocharged gasoline direct injection engine

This study analyzed the thermal balance of a turbocharged gasoline direct injection engine with intake air humidification and studied the reason why intake air humidification improved the thermal efficiency of the basic engine. The results showed that since the evaporation of the introduced water absorbed heat in the intake port that caused the decrease of the temperature of the intake air, and the specific heat capacity of working medium increased with intake air humidification. Therefore, an apparent decrease in the in-cylinder temperature. Each energy loss can be affected by intake air humidification in different degrees, among which the exhaust loss and heat transfer loss decreased evidently, while pumping loss and friction loss increased to some extent. Furthermore, the sum of the decrease of exhaust loss and heat transfer loss was higher than the sum of the increase of pumping loss and friction loss, hence, the thermal efficiency of the basic gasoline engine increased when the benefit gained from intake air humidification was greater than the negative impact.

Effect of gasoline aromatic compositions coupled with single and double injection strategy on GDI engine combustion and emissions

Gasoline direct injection (GDI) engines are facing the great challenge of particulate matter emission. In this work, three gasoline fuels meeting the latest China 6b gasoline standard but with different total and heavy aromatic contents were tested in a three-cylinder 1.0 L turbocharged GDI engine from the Chinese market. An experimental study of the single and double injection strategy on engine combustion, emissions and fuel consumption was conducted. The effect of the heavy aromatic components in the gasoline fuels was discussed in detail under different injection strategies as the Chinese market gasoline was abundant in aromatics for obtaining high octane number and there was no limit on heavy aromatics in the gasoline standard. The results showed that gasoline aromatic compositions were critical to the in-cylinder combustion and particulate emissions under the high-level emission operating conditions. The heavy aromatic contents presented a greater influence than the total aromatic content. It was also found that a late injection timing had significant negative impact on engine combustion, particulate emissions and fuel economy. Using the double injection strategy can reduce the particulate emissions, THC emissions and fuel consumption with all the test fuels, and the optimal strategy for low particulate emissions between different fuels was roughly the same. For the heavy aromatic fuel, compared with the results under the optimal single injection strategy, the particle number emission, THC emission and indicated specific fuel consumption were reduced by around 43.0%, 8.9% and 1.77% respectively under the optimal double injection strategy.

Investigation on low-speed pre-ignition from the quantification and identification of engine oil droplets release under ambient pressure conditions

• Engine oil viscosity does not have a determining effect on the oil droplets release. • Oil droplets release to the combustion chamber increases with the engine speed. • Working conditions of 2500 rpm and oil at 80 °C had the greatest amount of scrapped oil. • Image processing methodology applied to identify regions prone to appearance of oil. • Piston thrust and anti-thrust sides are critical regions for the appearance of oil. One source of low-speed pre-ignition in turbocharged gasoline direct injection engines is the presence of oil droplets in the combustion chamber. In this study, oil droplets released due to the piston reciprocating motion, have been quantified as function of oil viscosity and engine speed, by means of a motored test rig under ambient pressure conditions. Oil droplets were collected using a sandwich-like support and absorbing paper. An image processing methodology was developed to identify critical regions of the piston prone to the appearance of oil. Results show that oil is scrapped by the piston rings and released to the combustion chamber in zones transverse to the piston pin, at speeds as low as 500 rpm. Oil viscosity does not have a determining effect on the oil amount reaching the combustion chamber, while engine speed greatly increases this phenomenon, with a critical point at 2500 rpm and oil temperature of 80 °C.

Implementation of Optimized Artificial Neural Networks for Real-Time Estimation of Low Pressure Cooled Exhaust Gas Recirculation in a Turbocharged Gasoline Direct Injection Engine Using a Model-Based Design Approach

Abstract Low pressure cooled exhaust gas recirculation (LP-EGR) system has been widely adopted to improve energy efficiency in turbocharged gasoline direct injection (GDI) engines. In order to utilize complete beneficial effects of the LP-EGR, a technique capable of accurately observing the LP-EGR flow into the cylinder in real-time is a prerequisite. To precisely estimate the LP-EGR rate in real-time, this paper proposes artificial neural network (ANN) models and its implementation on a real-time embedded system. As inputs for the ANN models, 12 combustion parameters physically correlated with the LP-EGR in the combustion process are selected and calculated from the in-cylinder pressure. The ANN models for the real-time LP-EGR estimation were trained with the steady-state data of 30,000 cycles and their hyper-parameters were searched by a hyper-parameter optimization method. Moreover, a model-based design procedure is introduced to implement the optimized ANN models on the real-time embedded system. Since the proposed implementation performs the validation procedure for each process, it provides a systematic and seamless process for creating ANN models for real-time embedded systems. In real-time experiments under eight steady-state engine operating points, the embedded ANN models show the estimation performance with R2 of above 0.9716. The operation time of each ANN was less than 1.285 ms meaning that the target system can operate in real-time sufficiently with a mass-produced 32 bit microprocessor up to 256 MHz.

A comparative experimental study on emission characteristics of a turbocharged gasoline direct-injection (TGDI) engine fuelled with gasoline/ethanol blends under transient cold-start and steady-state conditions

In this study, the emissions of a TGDI engine were experimentally investigated and compared under transient cold-start operating and steady-state operating conditions, respectively. Furthermore, the steady-state emissions of the TGDI engine under different coolant out temperature (43 °C, 65 °C, 88 °C, 102 °C and 110 °C) were compared to the transient emissions. The results indicated that the transient NOx emissions and the steady-state NOx emissions were strongly depended on the load of the TGDI engine. Moreover, under steady-state operating conditions, the NOx emissions of the TGDI engine were increased with the coolant temperature from 43 °C to 102 °C, while the NOx emissions were decreased at the outlet coolant temperature of 110 °C due to retard the spark timing. Apart from that, the HC emissions under transient cold-start condition were approximately ten times than that of the steady-state conditions. Under steady-state operating conditions, the HC emissions were basically decreased with the coolant temperature from 43 °C to 110 °C due to reduction of the flame quenching distance. The excess air ratio of the TGDI engine slightly fluctuated around stoichiometric air/fuel ratio under the NEDC, while the excess air ratio was literally off the charts during the deceleration operating conditions due to the fuel cut-off. CO emission periodically reached a peak value at deceleration operating conditions under transient cold start condition, while CO emission was much high at the high-load and high-speed regions under steady-state operating conditions. In addition, the outlet coolant temperature did not present an obvious effect on the CO emission formation.

In-cylinder soot concentration measurement by Neural Network Two Colour technique (NNTC) on a GDI engine

In the present study, a new method named Neural Network Two Colour (NNTC) has been developed and applied to a turbocharged gasoline direct injection engine to directly analyze, within combustion chamber, most sooting conditions, by varying rail pressure and start of injection.The engine cylinder head was modified to create two sealed optical accesses for endoscope lighting and visualization, allowing image acquisition directly into combustion chamber. After an optical calibration of the system, several combustion images were acquired on 16 engine operating points with 8 levels of rail pressure and start of injection. The images were post-processed by the NNTC in order to calculate instantaneous soot production for each investigated operating point.The results demonstrated that the NNTC technique can be used as accurate method to detect soot production directly within combustion chamber. Moreover, by means of this method, it is possible to compute soot production in specific areas of combustion chamber.

Experimental study on the effects of the Miller cycle on the performance and emissions of a downsized turbocharged gasoline direct injection engine

The Miller cycle has been proven to be an effective way to improve the thermal efficiency for gasoline engines. However, it may show insufficient power performance at certain loads. In this study, the objective is to exploit the advantages of the Miller-cycle engines over the original Otto-cycle engines. Therefore, a new camshaft profile with early intake valve closure was devised, and two various pistons were redesigned to obtain higher compression ratio 11.2 and 12.1, based on the original engine with compression ratio 10. Then, a detailed comparative investigation of the effects of Miller cycle combined with higher compression ratio on the performance and emission of a turbocharged gasoline direct injection engine has been experimentally carried out based on the engine bench at full and partial loads, compared to the original engine. The results show that, at full load, for a turbocharged gasoline direct injection engine utilizing the Miller cycle, partial maximum power is compromised about 1.5% while fuel consumption shows a strong correlation with engine speed. At partial load, since the Miller effect can well reduce the pumping mean effective pressure, thus improves the fuel economy effectively. In addition, the suppression of the in-cylinder combustion temperature induced by the lower effective compression ratio contributes to the reduction of nitrogen oxide emission greatly. However, the total hydrocarbon emission increases slightly. Therefore, a combination of the Miller cycle and highly boosted turbocharger shows great potential in further improvement of fuel economy and anti-knock performance for downsized gasoline direct injection engines.