Experiment investigation on the performance and regulation rule of two-stage turbocharged diesel engine for various altitudes operation
Introduction
As altitude rises up, the density and pressure of atmosphere decreases rapidly so that less and less air flows into cylinder [1]. The naturally aspirated diesel engine loses 8–13% power and augments 9–14% fuel consumption with each increasing 1000 m [2,3]. Engine operating over 3000 m has barely been studied and more serious engine performance deterioration occurs on the plateau in China.
To enhance engine power and reduce fuel consumption at high altitude, two-stage turbocharging technology is viable to promote intake flow rate on the plateau [4]. Intake pressure ratio demand at 4500 m adds up to 4.4 as that at sea level approximately in the situation of fully intake flow rate regain. Such a great pressure ratio with a wide flow range for vehicle operation can hardly be achieved by a single-stage turbocharger, especially for diesel engine with high power density [5,6]. Two-stage turbocharging system is selected due to appropriate flow characteristics, which is able to provide adequate boost pressure to meet the intake need for full speed scope. Two-stage turbocharging system improves engine performance for full-load condition [7]. Furthermore, it results that the peak torque and the rated power of the two-stage turbocharged diesel engine increased remarkably, compared to the engine equipped with the single-stage turbocharger at altitude of 5500 m [8].
Two-stage turbocharging system is able to boost more air into cylinder and presents greater overall system efficiency at matching point or narrow operation area [9]. However, fixed turbocharging system (FGT) matched at high altitude behaves worse at low altitude. Vicente Bermu’dez1 et al. found that FGT increases engine pumping loss, reduces indicated efficiency of diesel engine at some operation area [10]. C.D.Rakopoulos reveals that two-stage turbocharged diesel engine saves fuel partly compared with single-stage turbocharged diesel engine. Nonetheless, with a too small HP turbine, it exhibits worse fuel consumption than single-stage turbocharger, which indicates turbocharging system should be regulated under different operation conditions [11]. Moreover, fixed two-stage turbocharging system matched for plateau issue is capable to satisfy the intake demand at high altitude, while it causes superfluous intake air into cylinder at low altitudes due to excessive boost ability [12]. Overpressure leads to a decline of engine performance and is not allowed for the sake of stable operation [13]. Therefore, two-stage turbocharging system must be regulated at lower altitude. Different regulation boundaries for two-stage turbocharging system at different altitudes exist and are unclear yet.
To acquire regulation strategy of two-stage turbocharging system at different altitudes, the influence of altitude on turbocharging diesel engine performance should to be investigated primarily. Shaohua Liu et al. researched the engine performance from 0 m to 2000 m. They summarized that with the decrease of atmospheric pressure, the brake specific fuel consumption increase creases when the pure diesel fuel is used [14]. However, only fuel consumption and smoke is explored, the other significant parameters of turbocharged diesel engine as well as the variation with altitude has not been involved. For turbocharged diesel engine, as altitude rises up, turbocharging system and diesel engine deviates from the original state at 0 m. Some papers aim to recover the engine performance at high altitude. They manifest that two-stage turbocharging system is able to achieve the recovery target at high altitude, such as 4500 m altitude [15]. Xin Shi et al. studied the influence of altitude on two-stage sequential turbocharged diesel engine by simulating [16]. Hualei Li et al. matched a two-stage turbocharging system for diesel engine and simulated the engine performance at high altitudes for boost pressure recovery [17]. Most of researcher focus on the engine performance at high altitude only, the effect of altitude on turbocharged diesel engine at various altitude is always neglected. Moreover, seldom articles care about the performance of turbocharging system and its effect on diesel engine at different altitudes. Ruilin Liu et al. [18] and Canova, Marcello, et al. [19] pointed out that traditional two-stage turbocharging system achieves great pressure ratio and wide operating flow range, but it is difficult to achieve optimal match result of traditional two-stage turbocharging system with diesel engine under all engine operating conditions, because the high-efficiency operation range is narrow. Carlucci Antonio Paolo et al. studied the engine performance at different altitudes with single-stage turbocharger, two-stage turbocharging system, single turbocharger combined with a mechanical compressor and single turbocharger with an electrically-assisted turbocharger by simulation. It reveals that two-stage turbocharging system is possible to reach the target power for each altitude and the fuel consumption will be further optimized by changing intake pressure ratio at various altitudes [20]. Ugur Kesgin proposed that the turbocharger efficiency for natural gas engine has great influence on the engine efficiency. An increase of 1% turbocharger efficiency brings an increase of around 0.08% in the engine efficiency [21]. Similar rule is appropriate for diesel engine. In short, most investigations focus on engine performance at high altitude, whereas, the effect of altitude on two-stage turbocharging system has always been neglected and they hardly refer to the influence of altitude on overall efficiency of turbocharging system, which is also critical for engine performance.
The regulation rule of turbocharged diesel engine at various altitudes is scarcely explored so that regulation strategy of turbocharging system at different altitudes is only obtained by numerous calibration. A. Chasse et al. developed regulation strategies for two-stage turbocharging system by simulation [22]. In recent years, some researches focus on regulation strategy of turbocharging system for various altitude operation. Hailei Zhang et al. [23] and Jun Wang et al. [24] studied the regulation strategy of a variable geometry turbocharger (VGT) for diesel engine. Simulation results show that, the performance of the engine, such as output torque and fuel consumption, can be improved significantly by optimizing the VGT opening. Based on same boost pressure at different altitudes, Katrašnik, T., and Trenc, F. present regulation boundary for single-stage turbocharger. The waste-gate will be generally opened when operating condition deviates from the matching point [25]. Xia Meng researched turbo-supercharging system to recover power of diesel engine at plateau by simulation. Adaption boundary and the switch point between these two modes were chosen according to the principle of maximum output torque [26]. It is a step adjustment system, and the switch point at different altitudes has not been proposed. Hossein Mansouri and Fatholah Ommi investigated the performance prediction of aircraft gasoline turbocharged engine at high altitudes. They concluded that indicated thermal efficiency varies with altitude and ambient temperature. The regulation strategy of waste-gate depends on the limit of engine operation, such as surge and chock boundary as well as intake and exhaust temperature of gasoline engine [27]. Nevertheless, they hardly refer to the effect of turbocharger performance or regulation rule on engine at various altitude. Form the point of regulation strategy, Zhang, Qingning, et al. investigates the effect of HP and LP turbo area on engine performance at different operation speed. They stated the HP turbo is more significant for low-speed operation and engine performance became more sensitive to the LP turbocharger. The regulation rule on turbocharging system has been overlooked [28]. Galindo, J., et al. [29] and Zheng, Zunqing, et al. [30] proposed the impact of the parameter on turbocharging system by the mean of thermomechanical analysis. They refer to the regulation rule of turbocharging system, but not the influence on dynamic and economic property of diesel engine, moreover, regulation strategy for various altitudes operation has not been mentioned. For turbocharged diesel engine, automatic compensation capacity is available for narrow altitude scope, but is unable to satisfy the intake demand of full altitude [31]. Mingyang Yang et al. analyzed available flow energy in a heavy-duty diesel engine as the altitude increases from 0 km to 4.5 km. It demonstrates significant effect of the altitude on the flow energy fed to the turbocharging system and energy split between two turbines [32]. This research concentrates on the energy transmission and distribution in turbocharging system, but hardly reveals the regulation ability of two-stage turbocharging system as well as the effect of regulation rule on the performance of turbocharging system or diesel engine. Regulating turbocharging system is valid to reduce pumping loss and enhance the indicated thermal efficiency of turbocharged diesel engine [33]. Regulation rules, including the regulation capacity and the effect on overall system efficiency, are not definite at different altitudes. Based on the research of regulation rules, the regulation strategy can be acquired and engine performance will be enhanced.
In brief, many papers concentrate on torque recovery at high altitude by matching suitable turbocharging system. However, it may result in engine performance deterioration at low altitudes, which is potential to be improved by regulating turbocharging system. The influence of altitude on diesel engine performance as well as regulation boundary of turbocharging system are not clear. Few papers focus on regulation rule, in terms of regulation capacity and overall efficiency of turbocharging system. The regulation rules make a significant contribution to enhance of output torque and reduction of fuel consumption at various altitudes, which should not be neglected.
In this paper, a control model for turbocharging system has been established, and the influence of altitude on turbocharging system and engine performance is investigated by experiment. Then, regulation rules on turbocharging system and diesel engine at different altitudes are acquired. The regulation boundary of turbocharging system is discussed. Finally, optimal related regulation area at various altitudes is proposed and engine performance will be improved, especially at low altitudes.
Section snippets
Engine performance test bench and altitude simulation system
The atmosphere parameter from 0 m to 4500 m are listed in Table 1, and main specifications of heavy-duty diesel engine are shown in Table 2. Two-stage turbocharging system should be matched for torque recovery at high altitude. According to the researches on matching method of two-stage turbocharging system [16,34,35], the matching point is selected at 4500 m under 1500r/min condition and equivalent turbo area is 13.22 cm2 by calculation. A H110 turbocharger is selected as high-pressure (HP)
The influence rule of altitude on diesel engine performance
Experiment of single-stage turbocharged diesel engine is conducted first. For a certain speed condition, fuel delivery will not reduce until engine operates unstably or reaches the restriction at high altitude, such as the limit of inlet temperature of HP turbo and turbocharger speed. The torque of 2200r/min and full-load condition at 0 m is reference condition, which is set as 1, and relative torque is the ratio between each condition and reference condition.
Output torque at five typical
Conclusions
In this dissertation, a control model for two-stage turbocharging system is developed, and a series of experiments are conducted on the environment simulation test bench. The following conclusions can be drawn from the work in this paper.
Performance of diesel engine has been discussed by experiment. Compared to single-stage turbocharger, fixed two-stage turbocharging system enhances the output torque at high altitude, whereas, brake special fuel consumption deteriorates at low altitude.
Declaration of competing interest
We have no conflicts of interest to declare.
Acknowledgements
This study is supported by the National Basic Research Program of China (973 Program) (Grant No. 61325202).
Notation
- A
- equivalent turbo flow area, m2
- Cp
- specific heat at constant pressure,J/ (kg·K)
- k
- adiabatic exponent
- m
- mass flow rate, kg/s
- P
- pressure, kPa
- T
- temperature, K
- efficiency, %
- pressure ratio / expansion ratio
- u
- valve opening, °
- V
- working volume, m3
- W
- power, kW
- μp
- proportional coefficient
- μi
- integral coefficient
Subscripts
- a
- intake air
- e
- exhaust
- T
- turbine
- C
- compressor
- TC
- turbocharging system
- tot
- total
- r
- reference state
- act
- actual valve opening
- sp
- target valve opening
- sat
- output value
- cly
- cylinder
- disp
- displacement
- ad
- adiabatic
Abbreviations
- BSFC
- brake specific fuel
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