Homogeneous Charge Compression Ignition Combustion: Challenges and Proposed Solutions

Engine and car manufacturers are experiencing the demand concerning fuel efficiency and low emissions from both consumers and governments. Homogeneous charge compression ignition (HCCI) is an alternative combustion technology that is cleaner and more efficient than the other types of combustion. Although the thermal efficiency and emission of HCCI engine are greater in comparison with traditional engines, HCCI combustion has several main difficulties such as controlling of ignition timing, limited power output, and weak cold-start capability. In this study a literature review on HCCI engine has been performed and HCCI challenges and proposed solutions have been investigated from the point view of Ignition Timing that is the main problem of this engine. HCCI challenges are investigated by many IC engine researchers during the last decade, but practical solutions have not been presented for a fully HCCI engine. Some of the solutions are slow response time and some of them are technically difficult to implement. So it seems that fully HCCI engine needs more investigation to meet its mass-production and the future research and application should be considered as part of an effort to achieve low-temperature combustion in a wide range of operating conditions in an IC engine

Fuel and combustion stratification study of Partially Premixed Combustion

Relatively high levels of stratification is one of the main advantages of Partially Premixed Combustion (PPC) over the Homogeneous Charge Compression Ignition (HCCI) concept. Fuel stratification smoothens heat releaseand improves controllability of this kind of combustion. However, the lack of a clear definition of “fuel and combustion stratifications” is obvious in literature. Hence, it is difficult to compare stratification levels of different PPC strategies or other combustion concepts. The main objective of this study is to define the fuel and combustion stratifications based on the fuel tracer LIF and OH* chemiluminescence images, respectively. A light duty optical engine has been used to perform the measurements. Four experimental points are evaluated, with injection timings in both the homogeneous and the stratified regimes. Twodimensional Fourier transforms of fuel distribution and chemiluminescence images provide the range of spatial frequencies in these images. This method gives the opportunity to separate a specific range of frequencies related to fuel and combustion stratification. The signal energy content in this range is used to define the stratification, using an appropriate normalization procedure. The results indicate that this new definition is a promising method to compare the level of stratification between different experiments

Analyzing of in-cylinder flow structures and cyclic variations of partially premixed combustion in a light duty engine

Partially Premixed Combustion (PPC) strategy offers the potential for simultaneously reduction of NOx and soot emissions with high efficiency. This low temperature combustion strategy involves a proper mixing of fuel and air prior to auto-ignition. During ignition delay (ID) the exact amount of premixing is crucial for the combustion behaviour and emission formation.In this article, high-speed particle image velocimetry (HS-PIV) has been applied to characterise the in-cylinder flow and cycle-to-cycle variations in a light-duty optical engine during fired conditions. The engine is operated at 800 rpm and at a constant CA 50 (~ 8 CAD aTDC). Multiple injections strategies (single, double and triple injections) have been applied to investigate their influence on the flow inside the piston bowl and squish region. The 2D velocity fields are evaluated and investigated over a range of crank angles in the compression and expansion strokes in order to understand the cycle-to-cycle variations. To investigate the problem of cyclic- variations on in-cylinder flows the phase-invariant proper orthogonal decomposition (POD) technique was used. The POD decomposition technique provides a classification method based on an energy criterion by which the mean flow is seen as a superposition of coherent structures. From their temporal coefficients it is possible to characterize its dynamical behaviour

Time-resolved in-cylinder PIV measurement in a light duty optical engine under PPC conditions

The understanding of in-cylinder flow field is one of the keys to realize Partially Premixed Combustion (PPC) for internal combustion engines, which has potential to achieve high combustion efficiency with low soot and NOx emissions. In this work, time resolved Particle Image Velocimetry (PIV) was performed to measure the flow field inside the cylinder of a single-cylinder light-duty optical diesel engine.The engine was modified to Bowditch configuration, and was installed with a quartz piston and a transparent cylinder liner, to allow optical access. The geometry of the quartz piston crown is based on the regular combustion chamber design of mass produced diesel engine, including a re-entrant bowl shape. This causes severe distortion on the obtained images, which has to be handled by a distortion correction method before PIV process.The in-cylinder flow structures in a vertical plane at the center of cylinder were obtained both within the piston bowl and within the squish volume, during the compression and expansion stroke. Measurements were performed under three different injection strategies as well as motored engine condition. Both the instantaneous flow field from single cycle and ensemble average flow field calculated from 100 cycles at motored engine condition show a well match with previous studies. The results from fired engine conditions show different Interaction between injected fuel and in-cylinder air at different Crank Angle Degrees (CADs) with different injection strategies.All the results in this study can provide a quantitative dataset being useful to model validation of numerical simulation work to investigate PPC engine more

Effects of intake temperature and equivalence ratio on HCCI ignition timing and emissions of a 2-stroke engine

Homogeneous charge compression ignition (HCCI) combustion, when applied to a gasoline engine, offers the potential for a noticeable improvement in fuel economy and dramatic reductions in NOx emissions. In this study, Computational Fluid Dynamic (CFD) is used coupled with detailed chemical mechanism (38 species and 69 reactions) for simulation of HCCI combustion of iso-octane and transitional flow inside the combustion chamber of a 2-stroke engine. Results show that increasing the overall gas temperature significantly advances the HCCI combustion timing. Concerning the equivalence ratio, by increasing it the ignition timing has been advanced and the maximum cylinder pressure has been increased. When equivalence ratio increases to more than 0.5 , NOx emissions significantly increases and go beyond 1000 [ppm]

Effectiveness of cognitive orientation to (daily) occupational performance (CO-OP) on children with cerebral palsy: A mixed design

Background. Cerebral palsy (CP) is the most common cause of physical disabilities during childhood. Therapeutic interventions mainly focus on impairment reduction to address motor-based difficulties. In contrast, Cognitive Orientation to daily Occupational Performance (CO-OP) is a cognitive approach, providing intervention at the level of activity and participation. Aims. This study aims to determine whether the CO-OP approach improves motor skills and achievement in motor-based occupational performance goals in children with CP. Methods and procedures. In this mixed design research (i.e., a multiple baseline single case experimental design and a one-group pretest-posttest design), five children with CP participated in 12 CO-OP intervention sessions. Repeated measures of motor skills for the multiple baseline single case experimental design were taken using the Bruininks-Oseretsky Test of Motor Proficiency (BOTMP); pre- and post-measures of parent/child perception of performance and satisfaction were identified using the Canadian Occupational Performance Measure (COPM); level of achievement was identified using Goal Attainment Scaling (GAS). Outcomes and results. According to the BOTMP results, all children were able to engage in the CO-OP intervention to improve motor performance. Significant differences after treatment were found in both performance and performance satisfaction ratings using the COPM as rated by parents and children. The GAS results showed progress in achievement levels for all children; all goals were achieved or exceeded. Conclusions and implications. CO-OP intervention can be helpful in improving motor skills and achieving self-identified, motor-based goals in children with CP

Biodegradable elastic nanofibrous platforms with integrated flexible heaters for on-demand drug delivery

Delivery of drugs with controlled temporal profiles is essential for wound treatment and regenerative medicine applications. For example, bacterial infection is a key challenge in the treatment of chronic and deep wounds. Current treatment strategies are based on systemic administration of high doses of antibiotics, which result in side effects and drug resistance. On-demand delivery of drugs with controlled temporal profile is highly desirable. Here, we have developed thermally controllable, antibiotic-releasing nanofibrous sheets. Poly(glycerol sebacate)- poly(caprolactone) (PGS-PCL) blends were electrospun to form elastic polymeric sheets with fiber diameters ranging from 350 to 1100 nm and substrates with a tensile modulus of approximately 4-8 MPa. A bioresorbable metallic heater was patterned directly on the nanofibrous substrate for applying thermal stimulation to release antibiotics on-demand. In vitro studies confirmed the platform’s biocompatibility and biodegradability. The released antibiotics were potent against tested bacterial strains. These results may pave the path toward developing electronically controllable wound dressings that can deliver drugs with desired temporal patterns