The fuel economy of recent small size DI diesel engines has become more and more efficient. However, heat loss is still one of the major factors contributing to a substantial amount of energy loss in engines. In order to a full understanding of the heat loss mechanism from combustion gas to cylinder wall, the effect of hole size and rail pressure under similar injection rate conditions on transient heat flux to the wall were investigated. Using a constant volume vessel with a fixed impingement wall, the study measured the surface heat flux of the wall at the locations of spray flame impingement using three thin-film thermocouple heat-flux sensors. The results showed that the characteristic of local heat flux and soot distribution was almost similar by controlling similar injection rate except for the small nozzle hole size with increasing injection pressure.
In the present work, a relative comparison of addition of water to diesel through emulsion and fumigation methods is explored for reducing oxides of nitrogen (NOx) and smoke emissions in a production small bore diesel engine. The water to diesel ratio was kept the same in both the methods at a lower concentration of 3% by mass to avoid any adverse effects on the engine system components. The experiments were conducted at a rated engine speed of 1500 rpm under varying load conditions. A stable water-diesel emulsion was prepared using a combination of equal proportions (1:1 by volume) of Span 80 and Tween 80. The mixture of Span 80 in diesel and Tween 80 in water was homogenized using an IKA Ultra Turrax homogenizer with tip stator diameter 18mm at 5000 rpm for 2 minutes. The water-in-diesel emulsions thus formulated were kinetically stable and appeared translucent. No phase separation was observed on storage for approximately 105 days.
Knowledge of the forces on the vehicle is necessary for designing most of the vehicle subsystems, however little knowledge of the dynamic forces on small off-road vehicles is available. To measure the vertical and longitudinal forces on the tires of an off-road vehicle, a custom strain gauge system was designed and combined with Quarq tire pressure sensors while running in off-road conditions. The strain gauge system consisted of a carefully calibrated half-bridge Wheatstone bridge of 350 Ohm resistors in bending, feeding the change in voltages into the 20-bit ADC of a Cypress Semiconductor PSoC 5LP microcontroller for data interpretation and then recorded onto an SD card for later analysis. The Quarq Tyrewiz tire pressure sensors were placed on both the front and rear tires and the recorded pressures were converted to forces on the tire through calibration and helped remove the uncertainty of certain strain gauge values. Experimental data was found to agree with suspension models.
Baja SAE is an intercollegiate competition where teams design and build a single-seat off-road vehicle that is powered by a small 10 HP Briggs & Stratton engine. Due to this power constraint, it is crucial to optimize the vehicle's weight and performance. The purpose of this paper is to demonstrate the process of simulating, designing, manufacturing, and testing the gearbox of the vehicle. The design process began by creating a vehicle dynamics simulation, which included engine performance, CVT Shifting, tire slipping, vehicle mass, rotational inertia, air drag, rolling resistance, weight shift, and drivetrain efficiency. These calculations predicted acceleration times, top speed, and optimal gear ratio. An often-neglected parameter that was analyzed was the rotational inertia in the drivetrain system. The results showed the effective mass of the vehicle increased 12% above the weight of the vehicle, primarily due to the weight and size of the CVT primary pulley.
Measuring brake emission is still a challenging non-standardized task. Extensive research is ongoing. Updates of work in progress are presented at SAE Brake Colloquium and PMP meetings. However, open items include how to achieve lower background concentration and how to design the brake enclosure. A low background concentration is essential as brake events are short and some emit in the range of reported background levels. Hence these emissions are difficult to distinguished from the background level. Even more critical, a high background concentration can result in a wrong particle number emissions value, either overestimated, background counted as emissions, or underestimated, background level subtracted, and low emission events no longer detected and counted. However, reducing the background level to less than 100 #/cm³ appeared to be quite challenging.
Vehicle NVH (Noise, Vibration and Harshness) is one of the most critical customer touchpoints which may lead to buying decisions. The importance of Noise inside the cabin is increasing day by day because of the new era of E-mobility and autonomous driving. Noise source could be the engine, powertrain, tyre, suspension components, brake system, etc. depending on driving conditions. Among these, tire noise is being identified as biggest contributor at constant mid-speed driving where engine and powertrain operate at minimum noise and wind noise is also at a moderate level. This driving condition becomes very significant for electric vehicles where engine noise is replaced by motor noise which is a tonal noise at very high frequency. This makes the improvement of tire noise levels quintessential for good cabin acoustic feel. This demands a proactive approach to develop low noise tire platforms for future mobility by leveraging research tools and best practices in the industry.
Raising demands towards lightweight design paired with a loss of originally predominant engine noise pose significant challenges for NVH engineers in the automotive industry. From an aeroacoustic point of view, low frequency buffeting ranks among the most frequently encountered issues. The phenomenon typically arises due to structural transmission of aerodynamic wall pressure fluctuations and/or, as indicated in this work, through rear vent excitation. A possible workflow to simulate structure-excited buffeting contains a strongly coupled vibro-acoustic model for structure and interior cavity excited by a spatial pressure distribution obtained from a CFD simulation. In the case of rear vent buffeting no validated workflow has been published yet. While approaches have been made to simulate the problem for a real-car geometry such attempts suffer from tremendous computation costs, meshing effort and lack of flexibility.
Autonomous vehicles must guarantee safety in all road conditions, including driving on wet roads. Aquaplaning (or hydroplaning) is a phenomenon known since the beginning of automotive history, never solved by an active safety system. Currently, no countermeasure system on the market is able to effectively counteract aquaplaning: ABS, ESP or TCS are still inefficient in overcoming this situation. Latest statistical data confirm that the higher percentage of accidents, injuries and deaths are caused by wet road conditions. The aquaplaning happens when the water on the road is too much and the tires start to float causing the instantaneous loss of control. Such phenomenon occurs in human-driven vehicles, with the responsibility of the driver, but in autonomous vehicles (e.g. Level 5), the responsibility for the safety depends on the car and the reduction of the speed is not a solution.
This work focuses on the effects of cooled Low Pressure EGR and Water Injection observed by conducting experimental tests consisting mainly of Spark Advance sweeps at different cooled LP-EGR and WI rates. The implications on combustion and main engine performance indexes are then analysed and modelled with a control-oriented approach, showing that combustion duration and phase and exhaust gas temperature are the main affected parameters. Results show that cooled LP-EGR and WI have similar effects, being the associated combustion speed decrease the main cause of exhaust gas temperature reduction. Experimental data is used to identify control-oriented polynomial models able to capture the effects of LP-EGR and WI on both these aspects. The limitations of LP-EGR are also explored, identifying maximum compressor volumetric flow and combustion stability as the main ones.