Developing a new V10 engine - an introduction

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Introduction

In the world of performance cars, the engine is considered the beating heart of the vehicle. Its mechanical characteristics, performance, and sound represent its “soul,” and a successful engine is often, if not always, decisive for the success of a model. Engines considered to be noble (V8, V10, V12, often naturally aspirated) have long been favored by manufacturers for their exclusive models.
However, with the advent of new environmental and noise reduction standards, new compact engines, often small-displacement V6 turbo hybrids, have emerged among prestigious manufacturers. Although these architectures are more powerful and efficient than the old V8, V10, and V12 engines, they do not provide the same pure mechanical sensations as the latter.
The Zephal ZC9 is a supercar concept currently in development. To power it with a “noble” engine while meeting various standards, it was decided to use the latter in combination with an electric architecture, which will be developed at a later stage.
This document describes the introduction of this engine project - the V1046AA/1 - including the main specifications, overall functional description, industrial objectives and constraints, technical choices used in the C202 block, and areas for improvement for the C203 version.

Position and role in the overall vehicle architecture

Figure 1 shows the position of the engine in the ZC9. The engine is a semi-structural component of the vehicle. The main monocoque ends behind the passenger seats, and two carbon side members, shown in blue on the diagram, are attached to it. Fasteners extend from the gearbox and connect to these struts, creating a rigid rear bay. To ensure optimal rigidity while facilitating ergonomics and maintenance, the engine connects directly to the rear of the monocoque and holds the electric motor/gearbox assembly in place.
In addition, it is necessary to reduce the engine's center of gravity as much as possible. It represents about 1/7th of the total weight of the vehicle and its positioning has a major influence on dynamic behavior. A low engine reduces pitching and rolling moments, thereby increasing vehicle performance. The last general consideration to consider is the thickness of the engine, which should be reduced as much as possible. To reduce aerodynamic drag and optimize airflow, the rear diffuser should ideally have ducts on the sides of the engine, directed towards the rear of the car. A thin engine allows for larger ducts, increasing performance and overall efficiency.

Figure 1 : Architecture of the Zephal ZC9

Development sequence

Development is simplified due to the inability to access sufficient resources - time, money, personnel -necessary for the complete and economically viable development of such a project. It is more of a proof of concept, a visibility model, and training for future similar projects.
The sequence (Figure 2) is divided into five main blocks corresponding to the main parts of the engine: the block, the lower crankcase, the two cylinder heads, and the intake. Between these blocks, essential calculation steps are carried out, as well as the implementation of the various circuits and initial calculations for the crankshaft. Finally, the final phase of development will focus on the elements related to these parts (gaskets, choice of bearings, sensors, etc.).

Figure 2 : Development sequence of V1046AA/1

This document covers the initial mechanical calculations, circuits, and engine layout. The initial calculations for the crankshaft will be examined in a future document, as they are necessary for the design of the crankcase. However, the final design of the counterweights will only be finalized after the pistons and connecting rods have been designed.

Main specifications

Defined specifications

Desired specifications

Architecture

Initial mechanical calculations

Displacement and stroke

The choice of a 4.6L 72° V10 engine with a bore x stroke of 94x67 was dictated by several considerations. The main one is emotional: a V10 is a compromise between the compactness and efficiency of a V8 and the power and nobility of a V12. Many remember the V10 era, from the late 1980s to 2005, as the “golden age” of Formula 1.
The 67mm stroke was chosen to be short enough to limit friction forces between the piston and cylinder and thus achieve high revs without mechanical damage. However, the bore/stroke ratio remains relatively conventional at 1.4. The 94mm bore is large enough to produce a large displacement and increase the heat exchange surface between the combustion chamber and its environment, without overly impacting the diffusion of the air/fuel mixture in the cylinder.

Engine speed calculations

In terms of figures, they are ambitious but realistic. To produce power P, we can adjust several parameters: displacement D, rotational speed ω, volumetric efficiency η_vol, air/fuel ratio λ, and specific fuel consumption BSFC.

Here, the displacement is set at 4.65L and the power at 500kW (680hp), giving a power density of 146 hp/L. This is considerable for a naturally aspirated engine, but some exceed 150 hp/L. The air/fuel ratio is set at 14:1, which is common for engines of this type. The 𝐵𝑆𝐹𝐶 and 𝜂𝑣𝑜𝑙 values are usually between 240g/kWh and 310g/kWh, and between 85% and 115%. By varying these values within this range, we obtain the engine speed required to develop 680 hp:

The formula governing the relationship between these values is given by:

The results of this equation give us this heat map (Figure 3). All values outside the triangle are excluded, so we will have to deal with this constraint later.

Figure 3 : Engine speed necessary to develop 500 kW

The 72° angle was chosen for three reasons. The first is that this configuration allows for natural balancing of primary vibrations, meaning that the sum of the pistons' inertial forces is constant. However, it is still necessary to balance secondary vibrations. Secondly, it allows the block to be thinner, which improves the vehicle's aerodynamics by freeing up space on the sides. The downside is that it raises the center of gravity compared to a 90° configuration. Finally, the harmonics developed by the regular explosions produce a melodious and distinctive sound.
A stroke of 67mm and a bore of 94mm were chosen to offer a good compromise between rotational speed, displacement, and rotating masses. With these values, inertial forces will be manageable at high revs while allowing maximum power of between 650 and 700 hp to be generated. By way of comparison, the V12 GMA Cosworth has a bore of 81.5 mm, a stroke of 63.8 mm, and a maximum power output of 670 hp at 11,500 rpm.

Circuits and integration

In an engine block, there are two main circuits to consider.

1- The oil circuit

2- The cooling circuit
These are auxiliary to the main volumes of the block (cylinders, engine crankcase) and are either molded or machined from solid material. Distribution is also critical and must be calculated from the outset so that the whole assembly can fit together correctly. Finally, it is important to consider gas leaks and the various components that need to be attached to the block (sensors, etc.).

The cooling circuit

Figure 4 : V1046AA/1 Cooling system diagram

The water circuit (actually a mixture of 50% water and 50% Glycol G13 or equivalent) is shown in Figure 4. The water pump is located on the right side and pumps water up into the engine through a gallery on the right side of the bench, which then opens onto a distribution duct located in the center of the V, a carbon insert. The use of an external part serves two purposes: to reduce the complexity of the center of the V, facilitating sand removal operations, and to lower the center of gravity. This solution is identical to that used on BMW's P82 engine, used in F1 from 2002 onwards (Figure 5).
The water returning from the cylinder heads is directed to the thermostat, also located on the right side of the engine for a short return to the water pump – the central position in Figure 4 is only there for clarity of the diagram. The hot outlet is routed to a single radiator.

Figure 5 : BMW P82 cooling system

Figure 6 : C202 block cooling system

Thermal dissipation calculations

The engine in its A/1 configuration produces a net power output of 680 hp, or 500 kW, which represents one-third of the total power delivered by the fuel.
The distribution of total power is shown in the graph below.

Figure 7 : Estimated repartition of energy

Thus, the total cooling required for the thermal part is 420 kW. Of this power, 65% comes from the water circuit, or 273 kW, and 25% comes from the oil circuit, or 105 kW. 10%, or 42 kW, is lost through radiation.
We therefore have 273 kW to dissipate directly through the cooling system. In order to absorb potential increases in power without resizing the system, a 20% increase in capacity is applied, bringing the total dissipation requirement to 327 kW.

Choosing the coolant

As the engine is intended for road use, the coolant chosen for this design is G13, a commercially available environmentally friendly propylene glycol-based additive.
The characteristics of the 50/50 G13/water mixture at 90°C are as follows:

Pump flow rate calculations

A single water pump, located at the bottom left of the engine, circulates coolant through the system. It must provide sufficient flow to effectively remove the heat generated by combustion.
We have :

𝑸̇ = 𝑚̇.𝐶𝑝.𝛥𝑇, where :

𝑸[𝑱/𝒔] 𝒐𝒖 [𝑾]̇ = Thermal power to dissipate, 𝑚[𝑘𝑔/𝑠]̇ = Mass flow, 𝐶𝑝[𝐽/(𝑘𝑔.𝐾)] = Thermal mass capacity, 𝛥𝑇[𝐾] = Water temperature difference

To evaluate the water pump, we will think in L/min and convert this equation into volume: 𝑚̇= 𝜌.𝑉̇, where:
𝜌 = Density(kg/m³)
𝑉 = Volume flow rate (m³/s), converted in L/min.
So :

𝑸̇ = 𝜌.𝑉̇.𝐶𝑝.𝛥𝑇, where :

𝑸̇=327000 𝑊, 𝜌 = 1065 𝑘𝑔/𝑚³, 𝐶𝑝=3450 𝐽/(𝑘𝑔.𝐾), 18𝐾<Δ𝑇<22𝐾 , taken at 20K for the initial calculations.

To find V, we reorganize the equation :

𝑽=𝑄̇/(𝜌.𝐶𝑝.Δ𝑇)

𝑽=327000/(1065.3450.20)

𝑽 = 0,00445 𝑚³/𝑠 = 4,45 𝐿/𝑠 = 𝟐𝟔𝟕 𝑳/𝒎𝒊𝒏

The pump must deliver a minimum flow rate of 267 L/min at maximum engine power, which corresponds to 16 m³/h.

The manometric height HMT, required to calculate the rotor diameter, is given by:
𝐻𝑀𝑇[𝑚]=(𝑈𝑝𝑝𝑒𝑟 𝑐𝑖𝑟𝑐𝑢𝑖𝑡 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒[𝐵𝑎𝑟]+𝑇𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 ℎ𝑒𝑖𝑔ℎ𝑡[𝐵𝑎𝑟]+𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑙𝑜𝑠𝑠𝑒𝑠[𝐵𝑎𝑟]).10
These values cannot be known precisely, so they are estimated based on similar vehicles at approximately 2.5 Bar, which gives an outer rotor diameter of approximately 120 mm.

Figure 8 : Water pump rotor diameters based on flow rate and pressure, graph by Fristam Pumps

The key specifications to remember for the rest of this document are therefore a flow rate of 267 L/min and a rotor diameter of 120 mm.

Oil circuit

The oil distribution system is heavily inspired by that of the Honda RA106E due to the existence of a document called F1 Special (The Third Era Activities) published by Honda R&D, which covers the optimization of the lubrication system in detail. For this engine, the oil flow requirement at 11,000 rpm is approximately 55 L/min (Figure 9). However, the displacement and therefore the surfaces to be lubricated are much smaller, at 2.4 L vs. 4.65 L for the V1046AA/1. Applying the same ratio between the required oil flow rates as that between 4.65 L and 2.4 L gives 106 L/min. The approximation is certainly simplistic, but the value of ~100 L/min is typical for this type of vehicle. According to the various sources consulted, the circuit pressure should be between 600 and 700 kPa.

Figure 9 : Necessary flow rate in the Honda RA106E

The oil circuit is shown in the diagram below. The feed pump supplies the oil filter, with a built-in bypass in case of overpressure. The oil is then distributed to the crankshaft and the three main galleries, supplying the crankshaft, cylinder heads, and piston nozzles. The oil returns from the cylinder heads, on either side of the block, back to the SCAV pump. The left cylinder head pipes feed directly into the manifold, while the right cylinder head pipes pass through a channel located under the dry sump.

On block C202, the conduits are positioned as follows. Please note that the holes supplying the distribution are shown in the 3D view, but not in Figure 10.

Figure 11 : CAD view of the C202 lubrication system

A few errors were identified in this initial modeling of block C202 and will be corrected in version C203, which will serve as the basis for developing the other engine components. The main errors are:

• Omission of the oil outlet port for the crankshaft, located below the filter outlet and routing to the timing cover
• Oil inlet located far to the right side of the block; a direct hole to the dry sump opposite the timing gear would be more appropriate
• Lubrication of a timing gear bearing located before the oil filter, which is very bad for particles
• Lubrication of the upper timing gear bearings (34/27 wheels) not modeled

Distribution calculations

In order to achieve high speeds exceeding 10,500 rpm without compromising engine reliability, it was decided to use a gear distribution system instead of a belt or chain. In addition to withstanding higher speeds, this method has the advantage of requiring no special maintenance and is designed to last the life of the engine. The main disadvantage is the cost of such a solution, which is justified on this high-performance engine. The calculation of the gear teeth meets several constraints, listed in order of importance:

    1- Transmission of rotation to the auxiliaries at the required ratios (exactly 0.5 for the camshafts, between 0.55 and 0.6 for the          water pump, and between 0.6 and 0.65 for the oil pump)
    2- Ensuring sufficient space for proper integration into the components (deck height, cylinder head height, etc.)
    3- Withstand stress and angular velocities
    4- Choose prime numbers for the number of teeth between two wheels in contact

The main thing is to first select the sequence of wheels leading to the camshafts. The height of the cylinder heads must be sufficient. To adjust the height, if necessary, the two 35-tooth idle wheels can be replaced with smaller or larger wheels as needed without affecting the transmission ratio. The speed ratio is calculated as follows:

The 35-tooth wheel is canceled out in the ratio calculation. We now need to determine the size of the assembly to satisfy the condition of a camshaft center height of approximately 330 mm. We have a choice of three modules for pinion distribution: M2, M2.5, and M3. Choosing a tooth size outside these standards would require the use of specific tools at a prohibitive cost. Adding the diameters of the wheels leading to the shafts gives us the following results: M2, M2.5, and M3. Choosing a tooth count outside these standards would require the use of specific tools at a prohibitive cost. Adding the diameters of the wheels leading to the camshafts, we obtain:

We therefore have the correct range of values with the M2.5 module. It should be noted that the actual assembly of the sprockets is slightly less extensive than the sum of all diameters, as their centers of rotation are not aligned in a straight line.
The water pump and oil pump ratios are simply defined afterwards. To define the correct ratios, we can test a few combinations close to the target values of 0.55 to 0.6 and 0.6 to 0.65 respectively.

The ratio of 0.581 was chosen to achieve a correct ratio while reducing the rotating mass and size compared to a 40-tooth wheel. In addition, 39 and 25 are prime numbers, which will improve the theoretical lifespan of the wheel. In practice, the wheels will be made of DLC-treated steel and will therefore have a service life that is more than sufficient for road use.
Regarding the oil pump:

The ratio of 0.648 was chosen to obtain a high pump speed while remaining within acceptable values. The 35-tooth solution may subsequently be changed to 36 teeth depending on the detailed modeling of the elements.

Block C202 pictures

The block is made of AlSi7Mg/A357 T6 aluminum, cast and then re-machined. A357 was chosen over A356 because of its higher torsional strength, with a value between 320 and 350 MPa for A357 alloys compared to 270 to 300 MPa for A356, at the cost of more delicate casting control.

Figure 13 : Galeries in the block

Figure 14 : Rear end

Figure 15 : Front end

Figure 16 : Underside

Figure 17 : Unreal Engine render

Conclusion

Designing a new engine is no easy task, especially when it involves a complex V-shaped architecture. These preliminary calculations lay the groundwork for the dimensions required for the assembly to function and thus for the direct modeling of the components. As stated in the introduction, the aim of the exercise is not to put this engine into production due to the limited economic and material resources available, but to create the most realistic architecture possible, providing a solid basis for future redevelopment and production, as well as for understanding the complex mechanical phenomena present in a V10.
The next iteration of the block, the C203, will correct the lubrication circuit errors present in the current C202.

References

(1) Honda R&D Technical Review F1 Special (The third Era Activities) – 2009 – P44-53; P276-277

(2) BMW Group Theissen-10-years-of-BMW-F1-engines – 2010

(3) Kevin L. Hoag Vehicular Engine Design 2nd edition - 2016