No abstract

Modern downsized internal combustion engines benefit from high-efficiency turbocharging systems for increasing their volumetric efficiency. However, despite the efficiency increase, turbochargers often lack fast transient response due to the nature of the energy exchange with the engine, which deteriorates the vehicle's drivability. An electrically-assisted turbocharger can be used for improving the transient response without any parasitic losses to the engine while providing energy recovery for increasing overall system efficiency. The present study provides a detailed numerical investigation on the potential of e-turbocharging to control load and if possible replace the wastegate valve. A parametric study of the optimum compressor/turbine sizing and wastegate area was performed for maximum torque, fast response time and energy regeneration across the real driving conditions speed/load area of the engine. The results showed that the implementation of a motor-generator could contribute to reducing the response time of the engine by up to 90% while improving its thermal efficiency and generating up to 6.6 kWh of energy. Suppressing the wastegate can only be achieved when a larger turbine is implemented, which as a result deteriorates the engine's response and leads to energy provision demands at low engine speeds.

Transient operation of turbocharged engines is mostly optimised in the light of quickness of response and the provision of the demanded torque. The time from demanded boosted torque to delivered torque above the maximum torque provided by the natural aspirated torque value is known as turbo-lag. This could reveal as an issue for small gasoline turbo-charged engines with a displacement of 1.0ltr or lower. These small types of engines are moving more and more in the focus for automobile applications. To provide the required power and torque, gasoline direct injection and turbo-charging are helpful in order to enable a reduction of fuel consumption by both de-throttled operation over a large area of operation and improved thermal efficiency among others achieved by maintaining an appropriate compression ratio. However, the application of a turbocharger especially on small engines drives also the back-pressure at the exhaust, in turn affecting the knock sensitivity of the combustion and thus impacting efficiency and power negatively. To achieve low levels of back-pressure even on small engines, the size of the turbocharger is from an efficiency point of view to be chosen of a rather large scale. In turn, a larger turbocharger increases the turbo-lag. Thus, an appropriate matching process of the turbocharger is a careful balance between efficiency, maximum torque and transient response, and in the light of stringent downsizing, this thematic deserves closer attention. The paper presents a new approach to characterise the transient operation and response behaviour of turbochargers while applying a new combination of established and novel approaches. Firstly, the interaction between vehicle parameter and shifted gear during acceleration is presented. The difference between the development of the torque delivered during transient operation compared to the steady state torque curve gathered from a dynamometer test of the engine is elaborated.Secondly, the turbo-lag is characterised by using the acceleration and corresponding jerk of the vehicle during an acceleration event. Based on these pre-requisites, the transient response of a C-car vehicle equipped with a smallengine is shown comparatively with a vehicle propelled by either a port-fuel injected natural aspirated gasoline engine or a turbo-charged diesel engine. Finally, a novel method to measure and analyse the turbo-lag using noise signals is presented. The advantage of this approach is that driveability and noise measurements can be done in parallel, leading to a reduction in set-up time and, moreover, allowing a more indepth analysis of the interaction of transient driveability and attributes. Furthermore, the relation between subjective perception and objective measured data is demonstrated.

No abstract

The homogeneous charge compression ignition (HCCI) gasoline engine promises low fuel consumption without expensive NO x aftertreatment. Owing to the self-ignition, HCCI has a faster combustion and therefore a higher level of vibration and acoustic excitation than DI-spark ignition (SI) engines. To effect a gasoline engine running in HCCI mode, residual gases must be trapped in the combustion chamber in HCCI mode. One solution to trap residual gases is to establish a negative valve timing overlap. This was done on a gasoline I4 engine, which is able to run in SI or HCCI mode by using independently controlled overhead camshafts. Noise and vibration analysis has been carried out on such an HCCI engine to quantify the impact of HCCI on the combustion and intake orifice noise. The noise and vibration analysis was done using either directly measured noise and vibrations from the development dynamometer or a noise prediction method based on recorded cylinder pressures and known transfer functions. The investigations were carried out at different speed and load points while changing control parameters such as intake cam timing, throttle, spark and injection timing and strategy. Using different data evaluation methods it was found that the HCCI mode with base settings can deliver higher NVH excitation than the SI mode at the same speed and load. However, by applying different combinations of control parameters, the NVH of the HCCI operation mode can be controlled in order to reduce its level of excitation and noise characteristics.