Life Cycle Greenhouse Gas Reduction Effects Induced by Turbocharger Multiple Remanufacturing in South Korea

Abstract

In light of growing global supply chain instability and carbon neutrality initiatives, South Korea has highlighted the need for a circular economy to reduce its reliance on natural resources. As a critical strategy for promoting a circular economy, remanufacturing has become essential because of its ability to improve resource efficiency and reduce environmental impacts. The automotive sector, which accounts for 80% of the remanufacturing industry, plays a critical role in these efforts. Turbochargers, primarily made of cast iron, represent approximately 20% of sales in this sector and are significant contributors to greenhouse gas emissions, making them an important target for emission reduction. This study examined the greenhouse gas emissions associated with turbochargers across multiple remanufacturing cycles using the LCA method. The results indicated an approximate decrease of 50%, 48%, and 46%, based on a comparative analysis between brand-new products and those remanufactured one to three times. Comparing brand-new and remanufactured products does not fully capture the key advantage of remanufacturing. This advantage lies in its ability to extend a product’s life cycle by using core parts as primary raw materials and reducing the consumption of new resources. Therefore, it is important to consider the environmental impact of remanufacturing within an expanded process, where brand-new products are included in the entire life cycle. Using this approach, the accumulated annual greenhouse gas reduction effect for multiple remanufacturing indicated decreases of approximately 25%, 32%, and 35% for remanufacturing one, two, or three times, respectively, compared to using only brand-new products. This study shows that multiple remanufacturing reduces greenhouse gas emissions compared to the use of brand-new products. In particular, as remanufacturing is repeated, the product lifespan can be extended from 3 years to up to 12 years with a concomitant decrease in annual greenhouse gas emissions. These findings provide valuable data for modeling and encouraging the greenhouse gas reduction potential driven by remanufacturing across various industrial sectors.

1. Introduction

Major countries worldwide are adopting various greenhouse gas (GHG) reduction policies as the awareness of climate change issues increases, including declarations of achieving carbon neutrality by 2050. Furthermore, as global supply chain instability intensifies alongside climate change, the Republic of Korea, a nation with limited natural resources, has proposed the “Promotion of Circular Economy” as one of its strategies to achieve carbon neutrality by 2050 [1].

A traditional linear economy, defined as “a sequence of processes from the acquisition of raw materials to manufacturing, use, and disposal”, neglects the concept of recycling, leading to resource depletion and environmental pollution [2]. In contrast, a circular economy emphasizes the reuse, remanufacturing, and recycling of materials from waste generated during the production process and end-of-life products. Among these, remanufacturing is increasingly being recognized as a critical tool for advancing a circular economy and related industries [3].

Remanufacturing involves disassembling, cleaning, inspecting, repairing, reconditioning, and reassembling used products to restore or enhance their original performance. These remanufactured products are then re-commercialized. In the resource circulation sector, remanufacturing has significant potential to reduce raw material usage and costs by minimizing the natural resources and energy required for production while demonstrating a superior environmental and economic performance [4].

In Korea, the “Act on the Promotion of the Conversion into Environment-Friendly Industrial Structure” introduces the circular economy concept, establishes certification for remanufactured product quality, and mandates labeling for these products [5]. These measures aim to promote the market launch of remanufactured products across various sectors and invigorate the remanufacturing industry through consumer protection measures such as labeling and quality certification.

The remanufacturing sector in Korea includes automotive parts, toner cartridges, construction machinery components, and machine tools. As of 2017, the market size of the remanufacturing industry was approximately KRW 1 trillion (approximately USD 885 million), reflecting approximately 30% growth compared to 2010 [6]. Among these, the automotive parts remanufacturing market is the most active, accounting for approximately 80% of the total remanufacturing market [7].

According to automotive remanufacturing companies, turbochargers, which are primarily composed of cast iron, have been identified as the largest item in the automotive parts remanufacturing sector, accounting for approximately 20% of the revenue. The steel industry, which produces and utilizes cast iron, contributes approximately 30% of GHG emissions in the industrial sector in the Republic of Korea [8]. Considering their high cast iron content, turbochargers hold significant potential to reduce greenhouse gas emissions in the steel industry by conserving raw materials and energy. Notably, the production of 1 kg of cast iron emits approximately 1.82 kg of CO₂eq. according to ecoinvent [9], highlighting the substantial environmental impact of cast iron manufacturing. Remanufacturing turbochargers, therefore, offers a critical opportunity to mitigate these emissions by decreasing the reliance on raw material production and lowering energy consumption.

Gao et al. [10] evaluated the environmental performance of turbocharger remanufacturing through a life cycle assessment (LCA). They analyzed the processes from raw material production to manufacturing and assembly to compare the environmental benefits of remanufactured turbochargers with those of new ones. On the other hand, Gao et al. [10] assumed that all components of turbochargers were 100% remanufactured, disregarding the realistic end-of-life stage. This assumption resulted in an inflated assessment of the environmental benefits and served as a significant variable in the LCA results, suggesting the need for a more realistic reflection.

Lee et al. [11] addressed this limitation by incorporating realistic remanufacturing ratios for core components, but their study only considered the greenhouse gas (GHG) reduction effects during a single remanufacturing cycle. While turbochargers are highly durable and frequently undergo multiple remanufacturing cycles, the impact of these repeated remanufacturing processes on the reuse rate of core components and the subsequent reliance on raw materials has yet to be thoroughly investigated.

This study hypothesized that multiple turbocharger remanufacturing cycles can reduce GHG emissions, even if the reuse rate of core components declines. It evaluated this hypothesis using a life cycle assessment (LCA) to analyze the potential effects.

Therefore, this study examined the accumulated annual GHG emissions associated with multiple remanufacturing cycles (more than three times for turbochargers) and assessed the resulting GHG reduction effects based on this analysis. By addressing this critical research gap, it provides a comprehensive understanding of the long-term environmental benefits of multiple remanufacturing, highlighting the GHG reduction potential that previous studies have not fully considered.

2. Turbocharger Components and Remanufacturing Process

2.1. Turbocharger Components

A turbocharger is an auxiliary device that improves engine output by compressing and supplying additional air to the cylinders. Heat resistance and durability are essential owing to the high thermal shock generated during this process. Therefore, turbochargers are made primarily of cast iron.

Figure 1 shows the six components of a turbocharger, including the intake housing, exhaust housing, bearing housing, turbine wheel, and centrifugal housing and rotor assembly (CHRA), which integrates the variable nozzle turbine (VNT) and actuator.

2.2. Turbocharger Remanufacturing Process

Figure 2 shows the turbocharger remanufacturing process. The remanufacturing procedure involves separating the collected used product (core parts) and cleaning, inspecting, and repairing the parts. Finally, the core parts are integrated with new components to assemble a complete turbocharger, which is then inspected.

3. Research Procedure

The LCA method was used to analyze the GHG reduction effects associated with the multiple remanufacturing of turbochargers. An LCA is an internationally standardized methodology specified in ISO 14040 and ISO 14044 [12,13]. The standards define four obligatory stages for executing an LCA goal and scope, life cycle inventory (LCI), life cycle impact assessment (LCIA), and interpretation.

The LCA quantified the resources and energy consumed, as well as the pollutants emitted throughout the product’s life cycle, providing a comprehensive assessment of the environmental impacts and identifying potential improvements.

In this study, the LCA method was applied to analyze the GHG reduction effects associated with the multiple remanufacturing of turbochargers.

4. Research Methods

4.1. Goal Definition and Scope

This study examined the accumulated annual GHG reduction effects resulting from the multiple remanufacturing of turbochargers. The target was the 4A480 turbocharger model used in the Hyundai Grand Starex (or commercial vehicles such as iLoad and iMax) [14,15], and the functional unit was one turbocharger. The life cycle of turbochargers depends on the driving conditions, engine load, and maintenance practices [16]. In particular, turbochargers may experience accelerated wear when operating in high-temperature and high-pressure environments for extended periods, making it difficult to generalize their life cycle [17,18]. Generally, the average life cycle of a turbocharger is at least 150,000 miles (approximately 240,000 km) [19].

According to remanufacturers, turbocharger replacements typically occur approximately every three years due to the mileage and engine usage conditions in commercial vehicles. The life cycle of a vehicle is approximately 15 years. Approximately five turbochargers are used during this period, considering the replacement cycle of turbochargers. However, a turbocharger can be remanufactured up to three or more times.

Based on these circumstances, this study analyzed the GHG reduction effects of turbocharger remanufacturing one to three times.

The system boundary encompassed a cradle-to-grave approach, covering all stages from raw material acquisition to end-of-use/life (Figure 3). Defining the system boundary often involves a significant volume of data, making complete data collection infeasible [20]. Narrower system boundaries facilitate easier data collection and ensure a higher data quality, focusing on processes relevant to the required information [21]. According to the cut-off criteria, up to 5% of the cumulative mass of the input materials can be excluded. In contrast, the contribution of each mass, energy, or environmental impact must not exceed 1%. In this study, the transportation stage was excluded from the system boundary due to its minimal contribution to both GHG emissions and cumulative mass. Similarly, the use stage was excluded because the high variability in consumer usage patterns makes generalization difficult.

The life cycle of a brand-new product (Life Cycle I) includes the stages of raw material acquisition, manufacturing, and end-of-use/life. In contrast, the life cycles of remanufactured products (Life Cycles II, III, and IV) integrate the life cycle of the remanufactured product and that of the previous product, encompassing raw material acquisition, manufacturing, and end-of-use/life.

A product remanufactured one time includes the life cycle of the brand-new product (Life Cycle I) and the product remanufactured one time (Life Cycle II).

A product remanufactured two times includes Life Cycle I, Life Cycle II, and the life cycle of the product remanufactured two times (Life Cycle III).

A product remanufactured three times includes Life Cycle I, Life Cycle II, Life Cycle III, and the life cycle of the product remanufactured three times (Life Cycle IV).

Remanufacturers collect used turbochargers (core parts) and disassemble them. They then clean, inspect, and repair the core parts. Consequently, in the case of remanufactured products, the raw material acquisition stage can be replaced with core parts, and components discarded from used products are disposed of within the remanufacturing life cycle. As a result, remanufacturing avoids the end-of-life of the previous life cycle and produces an extended process that includes multiple life cycles.

Hence, remanufacturing is a special stage that extends the life cycle of a product. For example, if a brand-new turbocharger ends after three years, a turbocharger that has undergone three remanufacturing cycles could last for up to twelve years. A significant advantage of remanufacturing is that it reduces the use of new resources because the core parts are used as the primary raw material, extending the product life.

4.2. Life Cycle Inventory Analysis

4.2.1. Raw Material Acquisition Stage

Table 1. Material weight and proportion list for a brand-new turbocharger.

Part Name		Materials	Proportion (%)	Weight (g)
Intake housing		Cast iron	95%	855
		Silicone	5%	45
Exhaust housing		Cast iron	95%	2565
		Silicone	5%	135
CHRA	Bearing housing	Cast iron	95%	1235
		Silicone	5%	65
	Turbine wheel and other part	Aluminum alloy	100%	650
VNT		Aluminum alloy	100%	500
Actuator		Stainless steel	50%	225
		Carbon steel	50%	225
Total				6500

lists the component materials and weight data for manufacturing a brand-new turbocharger, based on Lee et al. [10]. The major materials include cast iron, silicone, aluminum alloy, stainless steel, and carbon steel. The intake housing, exhaust housing, and bearing housing of the CHRA consist of 95% cast iron and 5% silicone. The turbine wheel and other parts and the VNT of the CHRA use 100% aluminum alloy, and the actuator is composed of 50% stainless steel and 50% carbon steel.

Table 2. Material weight and proportion list for remanufactured turbochargers.

Part Name		Materials	Proportion (%)	Remanufacturing 1		Remanufacturing 2		Remanufacturing 3
				Reman	New	Reman	New	Reman	New
Intake housing		Intake housing	Core	900	-	855	-	786.60	-
		Cast iron	95%	-	-	-	42.75	-	107.73
		Silicone	5%	-	-	-	2.25	-	5.67
Exhaust housing		Exhaust housing	Core	2700	-	2592	-	2436.48	-
		Cast iron	95%	-	-	-	102.60	-	250.34
		Silicone	5%	-	-	-	5.40	-	13.18
CHRA	Bearing housing	Cast iron	95%	-	1235	-	1235	-	1235
		Silicone	5%	-	65	-	65	-	65
	Turbine wheel and other part	Aluminum alloy	100%	-	650	-	650	-	650
VNT		VNT	Core	250	-	187.50	-	136.90	-
		Aluminum alloy	100%	-	250	-	312.50	-	363.10
Actuator		Actuator	Core	315	-	286.65	-	252.27	-
		Stainless steel	50%	-	67.50	-	81.68	-	98.87
		Carbon steel	50%	-	67.50	-	81.68	-	98.87
Total				4165	2.335	3921.15	2578.85	3612.25	2887.75
The proportion of brand-new and remanufactured parts replacement in turbocharger remanufacturing				64.08%	35.92%	60.33%	39.67%	55.57%	44.43%

lists the input/output data for the multiple remanufacturing of turbochargers. The data for the materials and weights of remanufacturing one time (remanufacturing 1) are cited from Lee et al. [10]. The input/output data of turbochargers remanufactured two or three times (remanufacturing 2 and 3) are based on the internal data from specialized turbocharger remanufacturers. The data for this study were collected from a single specialized turbocharger remanufacturer, which introduces certain limitations to the research. Additionally, the confidentiality of the remanufacturer’s data acts as a contributing factor. This reliance may have led to variability in the results, somewhat restricting the scope of the study.

For remanufacturing 1, the usage ratio of the core parts was approximately 64.08%, which decreased to 60.33% and 55.57% for remanufacturing 2 and 3, respectively. Hence, the damage rate of the core parts increased with multiple remanufacturing, reducing their use ratio compared to remanufacturing 1. Additionally, the turbine wheel and other parts and the VNT were entirely replaced with new materials during each remanufacturing process.

The decrease in the use of core parts was attributed primarily to turbocharger failures, often resulting from oil leaks. These leaks occur when engine oil escapes due to improper assembly between components, inadequate sealing, or aging. In addition, turbocharger failures are caused by defects within the turbocharger itself. For example, defects in the turbine wheel and other parts can cause damage to the inner walls of the intake and exhaust housing, and the exhaust housing combined with the VNT experiences shrinkage fitting caused by heat and cooling, making disassembly difficult over time. Consequently, some damaged components must be replaced with new ones.

4.2.2. Manufacturing and End-of-Use/Life Stage

In the manufacturing stage, this study used the electricity consumption data of brand-new turbocharger manufacturing and turbocharger remanufacturing from Gao et al. [10] and Lee et al. [11]. The electricity used to produce one turbocharger is 4.16 kWh for new products and 0.67 kWh for the remanufactured products.

In the end-of-use/life stage, this study referred to and processed the waste statistics data provided by KEITI [22] and applied the recycling, incineration, and landfill rates for waste metal and waste synthetic rubber, as listed in

Table 3. Proportion of recycling, incineration, and landfill for each type of waste.

Waste Type	Classes of Waste	Recycling	Incineration	Landfill	Others *
Cast iron	Waste metal (scrap iron)	98.00%	-	-	2.00%
Stainless steel
Carbon steel
Aluminum	Waste metal (non-ferrous)	99.67%	-	0.32%	-
Silicone	Waste synthetic rubber	93.80%	4.66%	0.03%	0.01%

* Others refers to intermediate disposal processes such as compression, crushing, and solidification.

. This study classified cast iron, stainless steel, carbon steel, and aluminum as “waste metal” and silicone as “waste synthetic rubber”, and applied their respective recycling, incineration, and landfill rates. The “others” category was excluded because it involves intermediate treatment rather than final disposal.

4.2.3. Life Cycle Inventory Database

The life cycle inventory database (LCI DB) aims to apply site-specific data. However, due to the challenges of collecting on-site data, this study, which focused on Korean data, utilized the LCI DBs provided by Korea’s Ministry of Trade, Industry, and Energy and the Ministry of Environment [23]. Where Korean datasets were unavailable, ecoinvent [9], a globally recognized international database, was employed.

Table 4. Applied LCI DBs and their sources.

Stages	Material	LCI DB	Source
Raw material acquisition	Cast iron	Cast iron production	ecoinvent 3.10
	Stainless steel	Stainless steel production	KEITI
	Carbon steel	Carbon steel production	KEITI
	Aluminum alloy	Aluminum alloy production, AlMg3	ecoinvent 3.10
	Silicone	Silicone product production	ecoinvent 3.10
Manufacturing	Electricity	Electricity production	KEITI
End-of-use/life	Cast iron recycling	Waste iron metal recycling	KEITI
	Stainless steel recycling		KEITI
	Carbon steel recycling		KEITI
	Aluminum alloy recycling	Waste non-ferrous metal recycling	KEITI
	Aluminum alloy landfill	Waste metal landfill	KEITI
	Silicone recycling	Mixed waste plastic recycling	KEITI
	Silicone incineration	Waste rubber incineration	KEITI
	Silicone landfill	Waste rubber landfill	KEITI

lists the LCI DB for the raw and subsidiary materials. The raw material acquisition stage utilized the same database as the corresponding materials listed. For the end-of-use/life stage, as detailed in Section 4.2.2, the databases were selected based on the classification criteria of waste for each material.

5. Life Cycle Impact Assessment

5.1. GHG Emissions for a Brand-New Turbocharger (Life Cycle I)

Table 5. GHG emissions of brand-new turbochargers in the product life cycle.

Components	Greenhouse Gas Emissions (gCO2eq./Unit)
	Brand-New (Life Cycle I)
	RM Acquisition	Manufacturing	End-of-Use	End-of-Life
Intake housing	1.78	0.0021	-	0.0082
Exhaust housing	5.34			0.025
Bearing housing	2.57			0.012
Turbine wheel and other parts	4.84			0.012
VNT	3.72			0.0089
Actuator	1.24			0.0017
TOTAL	19.50	0.0021	-	0.067
End-of-use	19.50
End-of-life	19.57

lists the results of the GHG emissions generated during the life cycle of a brand-new turbocharger (Life Cycle I). When a brand-new turbocharger reached the end of its life, it generated 19.57 gCO_2eq. In contrast, 19.50 gCO_2eq. in GHG emissions was produced when a brand-new turbocharger was remanufactured (end-of-use).

In the raw material acquisition stage, GHG contributions are significant in the order of the exhaust housing, the turbine wheel and other parts, and the VNT, while the actuator shows the lowest contribution. The exhaust housing accounts for approximately 42% of the total weight, resulting in high emissions. The turbine wheel and other parts and the VNT constitute approximately 10% and 8% of the total weight, respectively. On the other hand, the emission factor for aluminum alloy production in these components is approximately two to four times higher than that of cast iron and silicone. Therefore, they contribute significantly to GHG emissions, second only to exhaust housing.

In the end-of-use/life stage, GHG contributions were significant in the order of the exhaust housing, the bearing housing, and the turbine wheel and other parts. In contrast, the actuator made the lowest contribution. The analysis suggests that, consistent with the above results, the weight proportion and the emission factor of aluminum alloy contribute significantly.

5.2. GHG Emissions for Remanufactured Turbochargers (Life Cycles II-IV)

Table 6. GHG emissions of remanufactured turbochargers in product life cycle.

Components	Greenhouse Gas Emissions (gCO2eq./Unit)
	Remanufacturing 1 (Life Cycle II)				Remanufacturing 2 (Life Cycle III)				Remanufacturing 3 (Life Cycle IV)
	RM Acquisition	Manufacturing	End-of- Use	End-of- Life	RM Acquisition	Manufacturing	End-of- Use	End-of- Life	RM Acquisition	Manufacturing	End-of- Life
Intake housing	-	0.0010	-	0.0082	0.089	0.0010	0.00041	0.0086	0.22	0.0010	0.0092
Exhaust housing	-		-	0.025	0.21		0.00098	0.025	0.52		0.027
Bearing housing	2.57		0.012	0.024	2.57		0.012	0.024	2.57		0.024
Turbine wheel and other parts	4.84		0.012	0.023	4.84		0.012	0.023	4.84		0.023
VNT	1.86		0.0022	0.011	2.33		0.0028	0.012	2.70		0.012
Actuator	3.73		0.00015	0.0018	0.45		0.00018	0.0019	0.55		0.0019
TOTAL	9.64	0.0010	0.026	0.092	10.5	0.0010	0.028	0.094	11.40	0.0010	0.097
End-of-use	9.67				10.52				-
End-of-life	9.74				10.59				11.50

lists the GHG emissions generated by multiple remanufacturing. When the remanufactured product reached the end of its life, the GHG emissions generated for remanufacturing 1 (Life Cycle II), 2 (Life Cycle III), and 3 (Life Cycle IV) were 9.74 gCO_2eq., 10.59 gCO_2eq., and 11.50 gCO_2eq., respectively.

In contrast, when the remanufactured product was remanufactured again (end-of-use), the GHG emissions for remanufacturing 1 (Life Cycle II) and 2 (Life Cycle III) were 9.67 gCO_2eq. and 10.52 gCO_2eq., respectively.

The analysis showed that the emissions increased by approximately 8% with each multiple remanufacturing (Life Cycles III–IV) compared to one time remanufacturing (Life Cycle II). The remanufacturing rate decreased from 64.08% to 55.57% after one to three instances of remanufacturing, primarily due to technical limitations that constrained the ability to improve the remanufacturing rate, as the repeated use of remanufactured products results in increased damage to core components. Specifically, the remanufacturing rates of the intake and exhaust housings dropped from 100% to 87% and 90%, respectively, while those of the VNT and actuator declined from 50% and 70% to 27% and 56%. Consequently, multiple remanufacturing exacerbated durability issues, reducing component usability and increasing the demand for new parts. This ultimately diminished the overall greenhouse gas (GHG) reduction effect.

5.3. GHG Emissions for Multiple Remanufactured Turbochargers

Figure 4 shows the GHG emissions resulting from multiple remanufactured turbochargers, based on the comparative analysis between brand-new and remanufactured products presented in the study by Lee et al [11].

The GHG emissions generated for Life Cycle I were 19.57 gCO_2eq., 39.14 gCO_2eq., and 58.71 gCO_2eq., while those for Life Cycles II, III, and IV were 9.74 gCO_2eq., 20.26 gCO_2eq., and 31.69 gCO_2eq., respectively. Compared to Life Cycle I, these emissions indicate reductions of approximately 50%, 48%, and 46%, respectively. As explained in Section 5.2, remanufactured products experience increased damage to core parts relative to their initial manufacturing. This leads to the higher use of new parts during subsequent remanufacturing processes, reducing the GHG reduction effect.

As in Lee et al.’s study, comparing brand-new and remanufactured products does not fully capture the key advantage of remanufacturing [11].

This advantage lies in its ability to extend the product life cycle by using core parts as primary raw materials and reducing the consumption of new resources.

Therefore, it is important to consider the environmental impact of remanufacturing within an expanded process, where brand-new products are included in the entire life cycle. Since core parts from used products are sourced from new products, evaluating the environmental impact of remanufacturing requirements includes brand-new products in the life cycle assessment. This approach helps in accurately determining the accumulated GHG emissions.

5.4. Accumulated GHG Emissions for Multiple Remanufactured Turbochargers

Figure 5 shows the accumulated GHG emissions from the multiple remanufacturing of turbochargers. The life of a brand-new turbocharger (Life Cycle I) was three years; the life of a turbocharger involving multiple remanufacturing was extended to six, nine, and twelve years for Life Cycles II, III, and IV, respectively. The accumulated GHG emissions for Life Cycles I, II, III, and IV were 19.57 gCO_2eq., 29.24 gCO_2eq., 39.76 gCO_2eq., and 51.19 gCO_2eq., respectively.

As the turbocharger underwent multiple remanufacturing, the accumulated GHG emissions increased by approximately 9.67 gCO_2eq., 10.52 gCO_2eq., and 11.43 gCO_2eq. The increased use of new components during the multiple remanufacturing cycles also increased the GHG emissions.

Although the GHG emissions increased with remanufacturing, the process extended the life of the product significantly. Therefore, when a turbocharger is in use or replaced, selecting a remanufacturing product allows up to 12 years of use for a single turbocharger.

5.5. Accumulated Annual GHG Emissions for Multiple Remanufactured Turbochargers

The difference in life resulting from the number of remanufacturing cycles makes it challenging to compare and analyze the environmental impacts of products when based solely on accumulated GHG emissions. For example, a brand-new turbocharger has a life of three years, while a turbocharger that has been remanufactured three times can attain a life of up to twelve years. Therefore, evaluating these products based solely on accumulated GHG emissions, without considering their differing life, is inappropriate, overlooking the substantial environmental benefits of remanufacturing. Accordingly, this study calculated the decrease in the accumulated annual GHG emissions from all scenarios of the turbocharger’s life cycle to compare the emissions generated by each product over the same period, as shown in Figure 6.

As a result, GHG emissions decreased progressively with multiple remanufacturing. The accumulated annual GHG emissions for Life Cycles I, II, III, and IV were 6.52 gCO_2eq, 4.87 gCO_2eq, 4.42 gCO_2eq, and 4.27 gCO_2eq, respectively. Compared to Life Cycle I, these accumulated annual emissions indicate reductions of approximately 25%, 32%, and 35%, respectively.

These results suggest that multiple remanufactured products effectively reduce GHG emissions compared to brand-new products. In particular, the product life is extended, as remanufacturing occurs repeatedly, and the accumulated annual GHG emissions decrease. Hence, multiple remanufacturing processes contribute to reducing GHGs and conserving resources. This result contributes significantly to sustainability.

6. Discussion

This study analyzed the accumulated annual GHG emission reduction effects associated with multiple remanufactured turbochargers. The findings of this study are as follows:

① The GHG emissions for multiple remanufactured turbochargers were as follows:

(a)

As in Lee et al.’s study, comparing brand-new and remanufactured products showed that the multiple remanufacturing of turbochargers leads to a diminishing GHG reduction effect.

(b)

However, such comparisons do not consider a key advantage of remanufacturing, which is the reuse of core parts to reduce the need for new resources and extend the product life cycle.

(c)

Therefore, to accurately assess the environmental impact of remanufacturing, it is necessary to include the life cycle of brand-new products. Since core parts in remanufactured products originate from brand-new ones, they should be included within the system boundary. This approach allows for a more precise calculation of accumulated GHG emissions.

② The accumulated GHG emissions from multiple remanufactured turbochargers were as follows:

(a)

The accumulated GHG emissions for Life Cycles I, II, III, and IV were 19.57 gCO_2eq, 29.24 gCO_2eq, 39.76gCO_2eq, and 51.19 gCO_2eq, respectively.

(b)

Although the GHG emissions increased with multiple remanufacturing, the product lifespan was extended to up to 12 years. The lifespans of Life Cycles I (brand-new product), II, III, and IV were three, six, nine, and twelve years, respectively.

(c)

The differences in the life cycles of turbochargers resulting from different numbers of remanufacturing instances makes it challenging to compare and analyze the environmental impacts of products based solely on the accumulated GHG emissions. Therefore, this study also evaluated the annual GHG emissions to provide a more comprehensive understanding.

③ The accumulated annual GHG emissions resulting from the multiple remanufacturing of turbochargers were as follows:

(a)

The accumulated annual GHG emissions for Life Cycles I, II, III, and IV were 6.52 gCO_2eq, 4.87 gCO_2eq, 4.42 gCO_2eq, and 4.27 gCO_2eq, respectively.

(b)

These results indicate reduction effects of approximately 25%, 32%, and 35% for Life Cycles II, III, and IV, respectively, compared to Life Cycle I, confirming that multiple remanufacturing contributes to lower GHG emissions.

(c)

Hence, multiple remanufactured products effectively reduce GHG emissions compared to brand-new products. In particular, the product life increases as remanufacturing occurs repeatedly, and the annual GHG emissions decrease.

(d)

These results suggest that multiple remanufacturing processes can significantly enhance a circular economy and promote sustainability. Multiple remanufacturing helps reduce resource consumption and conserve resources through minimizing resource consumption and enhancing economic efficiency by extending the product life.

The results of this study provide a valuable model for understanding the GHG emission reduction effects of multiple remanufacturing in the case of turbochargers. The multiple remanufacturing of turbochargers achieved GHG emission reductions of up to 35% across successive life cycles compared to brand-new production, while significantly extending the product life and reducing annual emissions. These findings validate the hypothesis proposed in this study, confirming that multiple turbocharger remanufacturing cycles can reduce greenhouse gas emissions, even if the reuse rate of the core components declines. This highlights turbocharger remanufacturing as a practical example of how resource efficiency and environmental benefits can be maximized.

The results of this study demonstrate that multiple remanufacturing not only reduces GHG emissions, but also significantly decreases resource consumption. In the case of turbochargers, producing brand-new units up to three times requires a total of 19.5 kg of raw materials, whereas multiple remanufacturing reduces this to 7.8 kg. Additionally, through the reuse of core parts, multiple remanufacturing contributes to a reduction in waste and energy consumption, which are key strategies for achieving carbon neutrality [24].

This underscores the critical role of remanufacturing in carbon neutrality, highlighting its potential to enhance resource efficiency and reduce the environmental impact.

However, the proportion of parts that are completely discarded or replaced with new parts may increase when the damage rate of specific components is high during the remanufacturing processes or when remanufacturing occurs repeatedly. Improving restoration technologies is essential for minimizing the rate of new replacements and maximizing the GHG reduction effects of remanufacturing. The technologies currently used in remanufacturing, such as laser cladding [25] and 3D printing [26], exemplify the advanced technologies required for this purpose.

7. Conclusions

The LCA method was used to analyze the accumulated annual GHG emissions and the corresponding reduction effects associated with multiple remanufacturing processes applied to turbochargers. The findings provide a practical perspective on the remanufacturing industry, showing that enhancing the remanufacturing rate of products with a high steel content, such as turbochargers, can be an effective strategy for reducing GHG emissions in the steel sector.

The global shift toward carbon neutrality and a circular economy has brought growing attention to the remanufacturing industry. By restoring used products to their original performance, remanufacturing reduces the energy and resources needed for new production, cutting greenhouse gas emissions and significantly lowering the carbon footprint. Moreover, it empowers manufacturers to establish more efficient and sustainable production systems, yielding both environmental and economic benefits [27].

Moreover, the principles demonstrated in this study are transferable to other industries, as shown by evidence from sectors like smartphones, office furniture, small WEEE (waste electrical and electronic equipment), construction machinery, and batteries [28,29,30,31,32]. By emphasizing the broad applicability of remanufacturing, these findings underline its pivotal role in advancing circular economy practices and achieving sustainability goals across diverse industries.