Thermodynamic analysis on coupling characteristic of Twin-VGT and fuel injection parameters at variable altitudes

ABSTRACT

The decrease of inlet charge and mismatch of air and fuel are main reasons for the decrease of engine performance at variable altitudes. Understanding coupling mechanism between two-stage turbocharging and fuel injection system is key to maximize its potential for engine power recovery at variable altitudes. This paper focused on the coupling characteristic of twin variable geometry turbocharging (Twin-VGT) and fuel injection parameters on key parameters of gas path, in-cylinder combustion, and energy flow of the diesel engine at variable altitudes. Firstly, a thermodynamic cycle model of a Twin-VGT diesel engine aiming at variable altitudes was established and validated by experimental data. Furthermore, the coupling mechanism of high-pressure variable geometry turbocharging (HVGT) and low-pressure variable geometry turbocharging (LVGT) vanes on exhaust available energy (EAE), global expansion ratio (GER) and its distribution, global boost ratio (GBR) and its distribution, isentropic efficiency of the Twin-VGT, combustion process, and energy flow of the engine were studied at different altitudes. Enthalpy drop ratio is regulated by HVGT and LVGT and the isentropic efficiency of two-stage turbine reaches to maximum when openings of HVGT and LVGT at 0.35 and 0.75, respectively, at the altitude of 5500 m. Finally, this paper investigated the coupling characteristic of turbocharging and fuel injection parameters on combustion process and engine performance, which provides the theoretical basis for collaborative controlling of the Twin-VGT and fuel injection parameters at variable altitudes. Brake thermal efficiency (BTE) is affected by exhaust temperature which is mainly controlled by HVGT openings and injection advance angle (IAA) at variable altitudes, and BTE reaches to maximum when openings of HVGT at 0.4 and IAA at −5.5°CA under fixed engine load at the altitude of 5500 m.

KEYWORDS:

• Diesel engine
• Twin-VGT
• injection parameter
• coupling characteristic
• variable altitudes

Acknowledgment

The authors would like to acknowledge the National Natural Science Foundation of China (No. 52106192) and Military Scientific Research Projects (2021XXXXX423, 2021XXXXX424) for grants and supports.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Nomenclature

Notation

$p_{max}$	=	maximum in-cylinder combustion pressure(bar)
$\mathrm{T}$	=	temperature (K)
$\pi$	=	pressure ratio, expansion ratio
$\lambda$	=	pressure rise ratio, λ = 1.3~2.2
ε	=	compression ratio of diesel engine, ε = 12~20
$n_1$	=	compression polytropic index, $n_1$ = 1.35~1.37
$p_4$	=	boost pressure(bar)

Subscripts

ABE	=	acetone-butanol-ethanol
AFR	=	air-fuel ratio
BTE	=	brake thermal efficiency
BSFC	=	brake specific fuel consumption
CAS	=	combustion analysis system
CS	=	calibration system
EAE	=	exhaust available energy
EC	=	environmental chamber
ECS	=	engine control system
ECU	=	electric control unit
EGR	=	exhaust gas recirculation
ER	=	expansion ratio
EPCS	=	environmental pressure control system
FIQ	=	fuel injection quantity
FIP	=	fuel injection pressure
GBR	=	global boost ratio
GER	=	global expansion ratio
HP	=	high-pressure
HTIC	=	heat transfer in-cylinder
HVGT	=	high-pressure variable geometry turbocharger
IAA	=	injection advance angle
ICP	=	In-cylinder pressure
IMEP	=	indicated mean effective pressure
IHRR	=	instantaneous heat release rate
IT	=	intercooler
ITE	=	indicated thermal efficiency
MIP	=	mean indicated pressure
NOx	=	oxides of nitrogen
LP	=	low-pressure
LVGT	=	low-pressure variable geometry turbocharger
PCCI	=	premixed charge compression ignition
PL	=	pumping losses
PM	=	particulate matter
PMEP	=	pumping mean effective pressure
RU	=	refrigeration unit
SEPB	=	stable exhaust pressure box
TST	=	traditional two-stage turbocharger
VGT	=	variable geometry turbocharger

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [52106192]; Military Scientific Research Project [2021XXXXX423]; Military Scientific Research Projects [2021XXXXX423].