Turbocharger matching method for reducing residual concentration in a turbocharged gasoline engine

In a turbocharged engine, preserving the maximum amount of exhaust pulse energy for turbine operation will result in improved low end torque and engine transient response. However, the exhaust flow entering the turbine is highly unsteady, and the presence of the turbine as a restriction in the exhaust flow results in a higher pressure at the cylinder exhaust ports and consequently poor scavenging. This leads to an increase in the amount of residual gas in the combustion chamber, compared to the naturally-aspirated equivalent, thereby increasing the tendency for engine knock. If the level of residual gas can be reduced and controlled, it should enable the engine to operate at a higher compression ratio, improving its thermal efficiency. This paper presents a method of turbocharger matching for reducing residual gas content in a turbocharged engine. The turbine is first scaled to a larger size as a preliminary step towards reducing back pressure and thus the residual gas concentration in-cylinder. However a larger turbine causes a torque deficit at low engine speeds. So in a following step, pulse separation is used. In optimal pulse separation, the gas exchange process in one cylinder is completely unimpeded by pressure pulses emanating from other cylinders, thereby preserving the exhaust pulse energy entering the turbine. A pulse-divided exhaust manifold enables this by isolating the manifold runners emanating from certain cylinder groups, even as far as the junction with the turbine housing. This combination of appropriate turbine sizing and pulse-divided exhaust manifold design is applied to a Proton 1.6-litre CamPro CFE turbocharged gasoline engine model. The use of a pulse-divided exhaust manifold allows the turbine to be increased in size by 2.5 times (on a mass flow rate basis) while maintaining the same torque and power performance. As a consequence, lower back pressure and improved scavenging reduces the residual concentration by up to 43%, while the brake specific fuel consumption improves by approx. 1%, before any modification to the compression ratio is made

Waste heat recovery using a novel high performance low pressure turbine for electric turbocompounding in downsized gasoline engines: experimental and computational analysis

The development of a high performance LPT (Low Pressure Turbine) for turbocompounding applications in downsized gasoline engine is presented in this paper. The LPT was designed to fill the existing technology gap where no commercially available turbines can operate effectively at low-pressure ratios (1.05-1.3) to drive an electric generator with 1.0 kW power output. The newly designed LPT geometry was tested at Imperial College under steady-state conditions; a maximum total-to-static efficiency, ?t-s 75.8% at pressure ratio, PR ˜ 1.08 was found.The LPT performance maps were then used for a validated 1-D engine model in order to assess the effect of turbocompounding on BSFC (Brake Specific Fuel Consumption). Then a prototype of the LPT was tested in the post catalyst position on a 1.0 L gasoline engine for different operating conditions. The test results showed that reduction in BSFC of 2.6% could be achieved.With the post-catalyst position selected, a KP (key-point) engine speed/load analysis was performed in order to project an overall NEDC (New European Drive Cycle) fuel consumption benefit for the LPT in a mechanical turbocompounding configuration, as well as an overall power benefit calculation. Finally, a sensitivity study indicated what the power could be off-cycle

Automotive turbocharging

The future trends of automotive engine are universally toward down-sizing, higher power density and above all lower carbon emissions. Among many technologies revolutionizing automotive development, turbocharging is considered as a significant enabler to meet the ever increasing future demands. Uchida (2006) provided a good discussion on the future trends for the automotive industry and the inherent role of turbocharging, with focus on the Toyota research developments. Figure 1.1 shows the demand for specific power to increase to 70 kW/l and CO2 emission to reduce to 115 kg/km by the year 2010. Achieving the goal, according to Uchida (2006), will need technological steps forward with turbocharging enhancement as the main player. These views are also shared by Shahed (2005) in his article discussing the general demand and importance of turbocharging for the current and future automotive power train. Down-sizing and emission reduction were the main driving force behind the significant development of turbo diesels in Europe and similar development are predicted for the United States automotive industry

Influence of pulsating flow frequencies towards the flow angle distributions of an automotive turbocharger mixed-flow turbine

This paper aims to provide a detailed understanding of the flow interaction within the complex geometry of turbine stage coupled with reflection and superposition of the imposed unsteady pressure waves. The defining performance characteristic of a turbomachines is the inlet flow angle at its leading edge, which in most cases limit its optimum operational range. Pulsating flow field, typical to turbocharger turbine due to opening and closing of the exhaust valves, further deteriorates the flow angle distribution around its circumference, hence performance. To investigate this phenomena and how it differs from the steady state equivalent, a fully validated 'cold flow' Computational Fluid Dynamics (CFD) analysis was carried out. For this purpose, 4 unsteady CFD simulations of 20 Hz, 40 Hz, 60 Hz and 80 Hz together with the steady state simulations have been conducted at 30,000 rpm turbine speed. Discussions in this paper aim to provide a better insight on the flow angle behaviour in pulsating flow field. Evidences are shown where flow angle swings over a wide range (300% more than the steady state condition) in pulsating flow field as it propagates through the guide vanes. It was also found that the flow angle fluctuations during pressure drop period is significantly lower as compared to that during pressure increment period by (19°). This work also leads to a recommendation of correction factor in applying quasi-steady assumption of the rotor wheel. Without this correction, the prediction results could lead to underestimation of mass flow parameter up to 8% at high pressure rati