Search Results

The introduction of real driving emissions cycles and increasingly restrictive emissions regulations force the automotive industry to develop new and more efficient solutions for emission reductions. In particular, the cold start and catalyst heating conditions are crucial for modern cars because is when most of the emissions are produced. One interesting strategy to reduce the time required for catalyst heating is post-oxidation. It consists in operating the engine with a rich in-cylinder mixture and completing the oxidation of fuel inside the exhaust manifold. The result is an increase in temperature and enthalpy of the gases in the exhaust, therefore heating the three-way-catalyst. The following investigation focuses on the implementation of post-oxidation by means of scavenging in a four-cylinder, turbocharged, direct injection spark ignition engine. The investigation is based on detailed measurements that are carried out at the test-bench.

In this research, simulation and experimental investigation of H2 emission formation and its influence during the post-oxidation phenomenon were conducted on a turbo-charged spark ignition engine. During the post-oxidation phenomenon phase, rich air-fuel ratio (A/F) is used inside the cylinder. This rich excursion gives rise to the production of H2 emission by various reactions inside the cylinder. It is expected that the generation of this H2 emission can play a key role in the actuation of the post-oxidation and its reaction rate if enough temperature and mixing strength are attained. It is predicted that when rich combustion inside the cylinder will take place, more carbon monoxide (CO)/ Total Hydro Carbon (THC)/ Hydrogen (H2) contents will arrive in the exhaust manifold. This H2 content facilitates in the production of OH radical which contributes to the post-oxidation reaction and in-turn can aid towards increasing the enthalpy.

The objective of this study is to develop a practical technique to achieve HCCI operation with wide operation range. To attain this objective, the authors previously proposed the blowdown supercharge (BDSC) system and demonstrated the potential of the BDSC system to extend the high load HCCI operational limit. In this study, experimental works were conducted with focusing on improvement of combustion stability at low load operation and the reduction in cylinder to cylinder variation in ignition timing of multi-cylinder HCCI operation using the BDSC system. The experiments were conducted using a slightly modified production four-cylinder gasoline engine with compression ratio of about 12 at constant engine speed of 1500 rpm. The test fuel used was commercial gasoline which has RON of 91. To improve combustion stability at low load operation, the valve actuation strategy for the BDSC system was newly proposed and experimentally examined.

Conventional two-stroke engines have defects such as unstable combustion, high fuel consumption rate and high HC emissions. In order to overcome the defects, a direct fuel injection system and a novel scavenging system were adopted. The authors tested a newly developed reverse uniflow-type two-stroke direct injection gasoline engine that was designed by numerical simulations. In comparison with the base engine at low engine speed, HC emission was decreased by up to 80%, and BSFC was reduced by around 40%. Power and BSFC were superior to those of a latest port-injection four-stroke engine. Furthermore, it was found that engine performance of exhaust gas emissions, fuel economy or output power can be selectively optimized by switching homogeneous and stratified combustion.

To survive the severe regulations for both the exhaust gas emissions and fuel economy, research on small two-stroke gasoline engines from both the experimental and theoretical viewpoints is quite necessary. In the present study, firstly, performance tests of a direct injection small two-stroke gasoline model engine were carried out. Based on these experimental results, three-dimensional flow calculations from scavenging pipe to exhaust pipe during the gas-exchange and piston compression processes were made with the same experimental conditions. As a result, the gas exchange process was investigated and some problems were clarified. Secondly, parametric calculations with changing just exhaust port timings were performed to solve the problems found in the above calculations.

In this research, a novel methodology for the post-oxidation in a turbocharged spark ignition (SI) engine is proposed and investigated that can improve the emissions along with the reduction in turbo-lag. In this research, both simulation and experimental activities are performed. The 1-D simulation model was used for the identification of efficient scavenging. Thereafter, experimental validation tests for modeling and post oxidation were conducted on a 4-cylinder turbocharged SI engine. From the results, it was revealed that efficient scavenging and post-oxidation can be obtained at lower speed and higher load. The enthalpy in exhaust manifold increased due to the post-oxidation reaction which in turn increased the temperature and pressure of the exhaust gases and hence emissions reduced. Also, due to the increased enthalpy at turbine upstream, the turbocharger speed increased and as a consequence, reduction in the turbo-lag was observed.

Resistive particulate matter sensor (PMS) is a promising solution for the diagnosis of diesel/gasoline particulate filter (DPF/GPF) functionality. Frequently triggered regeneration of their sensing element, for cleaning the soot dendrites deposited on the surface, leads to experience high temperature and thermal stress and pose high risk of developing cracks in the electrodes or sensing substrate. A semiconductor with a dopant concentration of 100 ppm~10000 ppm is applied as a sensing element for PMS self-diagnosis. Upon cooling at air, the polarization doped-insulating layer in a resistive PMS starts to resume the electrical conductivity in the wake of experiencing high regeneration temperature, through the electron and hole directional mobility.

There is a growing need for low-emissions concepts due to stricter emission regulations, more stringent homologation cycles, and the possibility of a ban on new engines by 2035. Of particular concern are the conditions during a cold start, when the Three-Way Catalyst is not yet heated to its light-off temperature. During this period, the catalyst remains inactive, thereby failing to convert pollutants. Reducing the time needed to reach this temperature is crucial to comply with the more stringent emissions standards. The post oxidation by means of secondary air injection, illustrated in this work, is a possible solution to reduce the time needed to reach the above-mentioned temperature. The strategy consists of injecting air into the exhaust manifold via secondary air injectors to oxidize unburned fuel that comes from a rich combustion within the cylinder.

Experimental methods and numerical analysis were used to investigate the mechanism of high-speed knocking that occurs in small two-stroke engines. The multi-ion probe method was used in the experiments to visualize flame propagation in the cylinder. The flame was detected by 14 ion probes grounded in the end gas region. A histogram was made of the order in which flames were detected. The characteristics of combustion in the cylinder were clarified by comparing warming up and after warming up and by extracting the features of the cycle in which knocking occurred. As a result, regions of fast flame propagation and regions prone to auto-ignition were identified. In the numerical analysis, flow and residual gas distribution in the cylinder, flame propagation and self-ignition were visualized by 3D CFD using 1D CFD calculation results as boundary conditions and initial conditions.

This study aimed to achieve both a high compression ratio and low knock intensity in a two-stroke engine. Previous research has suggested that knock intensity can be reduced by combining combustion chamber geometry and scavenging passaging design for the same engine specifications with a compression ratio of 13.7. In this report, we investigate whether low knock intensity can be achieved at compression ratios of 14.4 and 16.8 by adjusting the combustion chamber geometry and scavenging passage design. As a result, the mechanism by which combustion chamber geometry and scavenging passage design change knock intensity was clarified.

Post-oxidation has been used to enhance the chemical reactions in the exhaust gas pipes, leading to the activations of the turbocharger and catalyst at cold state. In this research, a detailed study of the various mechanisms for post-oxidation is performed. For the post-oxidation activation, the unburned gas species (CO, THC, H2) in the exhaust manifold must be produced by some methodologies, such as scavenging, lambda-split, and post-injection. The required amount of O2 concentration can be either supplied by the scavenging (valve overlap tuning) or the secondary air injection (SAI) system. Mixing the species is also an important key to promoting post- oxidation, and an internal bypass adapter with a modified exhaust adapter shape was developed and evaluated.